# Altimeter/GPS question from the skyrocket guy...

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#### John Ross

##### Active Member
The continued lockdowns and cancellation of events locally and nationwide have resulted in me having more free time on my hands to do research. After getting such helpful, immediate, and useful advice on OpenRocket software from the people in this group, I thought I'd pose another question.

Before I do, let me explain that I have a learning disability when it comes to anything with wires. Replacing a common light switch is about the upper limit of my abilities where electricity is concerned.

I read with interest the pinned topic on altimeters and GPS units suitable for rocketry. However, the last post in that thread was from 2018, and I thought that some things might have happened since then.

How many of these units are useful in situations where you know in advance that you are not going to be able to retrieve the unit after the flight?

The annual PGI convention that was scheduled for next month, and for which I have been preparing entries for the "best rocket motor" competition, has been canceled. I've got another year to up my game.

Judging criteria for "best" rocket motor is comprised of a variety of factors, of which altitude is only one. However, even if it's not in the rulebook, there's a lot of friendly ribbing among amateur pyrotechnicians about who can build the highest flying motor, or the one that goes the highest on a given amount of fuel.

I assume there are now units that will send information to a smartphone or pad device in real time, and not depend on physically retrieving the unit after the flight and plugging it into a computer with a USB cable in order to download the data.

Are any such units cheap enough for one-time use? There are a lot of us who spend thousands of dollars and hundreds of hours preparing for and attending the annual convention, just as I'm sure it is with you guys in HPR events. Another couple hundred bucks for a fistful of altimeter/GPS units is something I believe a lot of people, especially competitors, would add to their budgets for the PGI convention.

If some kind of "find me" function were included, we might even get them back when working cleanup crew the next morning at the fallout zone...

JR

#### neil_w

##### Hunkered down and slowly going crazy
TRF Supporter
Interesting question.

Just my own opinion: I would not want electronics raining down as litter after a flight, from an environmental standpoint. Do folks do this now?

#### BEC

##### Well-Known Member
That is an interesting question. There are a number of relatively inexpensive GPS-based units that will telemeter position (see Eggfinder products for kits), but you're looking for altitude telemetry. The least expensive device I can think of that does that is the TeleMetrum TeleMini: http://shop.gag.com/home-page/telemini-v3.html

This requires a ground station of course, as well as an amateur radio ("ham radio") technician's or above license.

At $150 for the airborne unit (plus a battery to run it) it's certainly not cheap enough for me for one-time (intentional) use. Your budget may be different . Others may chime in for license-free solutions. And there may be some cellular-based solutions IF you have cell service at your "launch" site. #### John Ross ##### Active Member Just my own opinion: I would not want electronics raining down as litter after a flight, from an environmental standpoint. Do folks do this now? LOL! I like to think that I'm an imaginative person who comes up with thoughts and ideas that most other people haven't considered. It's an important skill set to have if you want to be a successful writer of political thrillers and other popular fiction. That said, I would never have anticipated your response to my question. Do you worry about the broken or obsolete cell phones or microwave ovens that consumers throw away every day? ;-) FYI, pyrotechnicians today use exactly the same construction methods and materials that their predecessors employed in past centuries. 99.99% (and I am not exaggerating here) of the materials we use are environmentally friendly. Besides the pyrotechnic compositions we employ (which are entirely consumed during the effect), every firework we construct is made of Kraft paper, chipboard, or other similar paper product, cotton or hemp twine, wheat paste, hide or fish glues (in addition to woodworker's glues like Titebond), bentonite clay, tar, wood, and other natural and biodegradable materials. No firework I have ever constructed used any plastic at all. Off the top of my head, the only thing I can think of that doesn't fit this narrative are the 1" squares of aluminum foil (HVAC) tape I use for chain fusing. I'd estimate that the entire amount of such product that I use in one of my annual shows is less than the quantity of aluminum foil a person would use while cooking a single turkey for a family dinner. At any club shoot, and especially at the weeklong PGI convention, a cleanup crew goes out early every morning to the "fallout zone" of the shoot site. The main thing we are looking for is unexploded aerial shells whose time fuses failed to take fire. These ball shells are now lying on the ground. Policing them up is the number one priority of the safety crew. Failed firework shells are miniature versions of the dud artillery rounds common to former war zones, except they don't bury themselves deep in the earth the way military ordnance does. In addition to unexploded shells, the crew gathers up any litter present. This consists almost entirely of expended skyrockets and sticks. The bigger rockets use Poplar sticks that are an inch square and five feet long. In the scenario where some rocket builders might use electronic devices on their rockets in the PGI competition, I imagine there might be a few key-fob-sized electronic dohickeys in the fallout zone, and the crew would pick them up. This strikes me as a trivial consideration. We're not talking about Skylab de-orbiting here… Consider that every spectator at the convention stopping at the Quick Mart on the way home is likely to generate more trash than the rocket guys, just by buying a Big Gulp in a Styrofoam cup with a plastic straw, a candy bar, and some bottled water. Back on the subject of rocket building, is there a way for the OpenRocket software to simulate a rocket using three sticks, with a few inches of cardboard tube encircling their bottom ends to shift the CP rearward and thus enhance stability? BTW I am having a grand old time doing simulations on this software. Many thanks once again for your considerable help and expertise! JR #### neil_w ##### Hunkered down and slowly going crazy TRF Supporter That said, I would never have anticipated your response to my question. Do you worry about the broken or obsolete cell phones or microwave ovens that consumers throw away every day? ;-) I certainly don't throw them on the ground and leave them there, and would have an issue with anyone who does. If the expended shells and/or rockets or whatever are collected at the end of the day, then I would have no problem with it. I am unfamiliar with fireworks standard practices. Certainly, in hobby rocketry, there is a strong ethic of minimizing litter left on the field, particularly anything toxic or non-biodegradable. Back on the subject of rocket building, is there a way for the OpenRocket software to simulate a rocket using three sticks, with a few inches of cardboard tube encircling their bottom ends to shift the CP rearward and thus enhance stability? BTW I am having a grand old time doing simulations on this software. Many thanks once again for your considerable help and expertise! OR can't do tail rings, at least it can't simulate them. Common practice to *visually* model a tail ring and include it in CG calculation is to use an "internal tube", which can be made as large as desired (so as not to be internal) and positioned anywhere. Rocksim has full support for them. Can you take a screen snap of the design you're talking about? I'm still having a bit of trouble picturing it. #### John Ross ##### Active Member OR can't do tail rings, at least it can't simulate them. Common practice to *visually* model a tail ring and include it in CG calculation is to use an "internal tube", which can be made as large as desired (so as not to be internal) and positioned anywhere. Rocksim has full support for them. Can you take a screen snap of the design you're talking about? I'm still having a bit of trouble picturing it. Drawn freehand on a pizza box on my lap. Rocket motor with ball on top, and three 1/4" square sticks (might use bamboo skewers) with a cardboard tube glued around their ends. Normal practice would be to use a single stick that would be both thicker and longer than shown here. JR #### neil_w ##### Hunkered down and slowly going crazy TRF Supporter Got it. Yeah, OR unfortunately can't do what you need there. You can try downloading Rocksim and using the free trial for a little while to get an idea of how that'll behave. Tail rings are draggy but do great things for stability. Honestly, though, I'm not really sure if that design conforms to the assumptions that OR (or Rocksim) would normally make about rocket geometry; it's pretty far outside the usual. So take whatever results you get with a grain of salt. Building one and doing some test flights would probably be a good idea. #### tsmith1315 ##### Well-Known Member Certainly, in hobby rocketry, there is a strong ethic of minimizing litter left on the field, particularly anything toxic or non-biodegradable. That said, I would never have anticipated your response to my question. Do you worry about the broken or obsolete cell phones or microwave ovens that consumers throw away every day? ;-) John, Neil's reaction is par for the hobby. What I see as "standard rocketeer point of view" is that of a group of people who have begged permission to gather on someone else's property and have a good time for a couple of days on a regular basis. I imagine the landowner looking out and seeing 50 cars, tents, a PA system, a crowd of strangers and a bunch of smoke in his field for the first time... Environment and ethics aside, we appreciate their courtesy and want to continue using their fields. That tends to guide our perspective a bit. #### John Ross ##### Active Member Oh, I'm with you on that. We fireworks guys have stuff that is more dangerous and much noisier than model rockets, so finding shoot sites is even more of a challenge for us. We police up all litter, just like you. My initial reaction was that Neil was upset about electronics ending up in a landfill. After all, a sticker on the side of your skyrocket altimeter saying "$50 REWARD FOR RETURN! Call (XXX) 555-1234" would eliminate any claim that one was "littering."

The Gold Standard for this issue is Oshkosh. Go to the fly-in there and see a half a million people, beautiful airplanes, and NO litter. Heart-warming.

JR

#### neil_w

TRF Supporter
My initial reaction was that Neil was upset about electronics ending up in a landfill. After all, a sticker on the side of your skyrocket altimeter saying "$50 REWARD FOR RETURN! Call (XXX) 555-1234" would eliminate any claim that one was "littering." No, it was about littering the field. Cleared up now, we can move on. The Gold Standard for this issue is Oshkosh. Go to the fly-in there and see a half a million people, beautiful airplanes, and NO litter. Heart-warming. That is a magnificent event, and I feel fortunate to have been able to go one year. It is hard to describe the feeling of seeing huge squadrons of WWII aircraft flying overhead, but I suppose it starts with awe. #### NateB ##### Well-Known Member I have made sims for stick rockets using a single fin with the dimensions and weight of the stick used. Using 2 or 3 sticks is as easy as creating the shape of the fin with the options and selecting the number of fins and correct orientation of them. I'm not really Open Rocket deals with the stability of it correctly. I'm working on a project now with a 5" hemi and 24mm motor mount to send up an altimeter with full recovery. Obviously, no pyrotechnic heading on this one, but I am curious about the data from the altimeter. If I can recover and resue them, the next step is to scale up and send up the 1" K+Benz whistles I like to make. #### ksaves2 ##### Lifetime Supporter TRF Lifetime Supporter Ummmmm, Quick question here. Define ”best rocket motor”. Are you restricted to compressed BP formulas or is ammonium perchlorate composite propellant allowed? If so APCP will win hands down period. I’m not a pyro guy but there are issues with getting larger BP motors to work reliably. One imperfection in the compressed BP and they have a tendency to go kaboom. Unless PGI considers the best CATO in their scoring I wouldn’t think that would be the path to travel (ie. BP motor). A few micro bubbles in APCP propellant and an erosive nozzle can do wonders for a motor that still performs (albeit at maybe a higher burn rate), gives perhaps a better performance without over pressurizing and rupturing the casing. I always thought for shells an explosive lifting charge was used? Why is PGI going with a best rocket motor category? I would think the commercial rocket motor makers have already been there and no need to make the mistakes already made “all over again”. There’s a reason why one doesn’t see F or higher impulse BP motors being commercially made. A lot of trouble for consistency. I don’t think anything higher than a BP ”F” was ever available? Oldsters correct me if I’m wrong. For entertainment purposes, I would find an event like biggest and “bestess” BP motor a lot of fun as long as it was in the right venue with safety first and foremost. Another thing to consider is with pyro, I suspect all the stuff that goes into a display shell is designed to do it’s job and leave a small residue when it’s done ie. turn into confetti. With larger rocket motors a disposable rocket casing without a recovery device could be a hazard in the wrong venue. Is one in this competition supposed to loft a display shell with said rocket motor or is it simply just “fly a rocket motor”? If it’s simply fly a rocket motor, if APCP is allowed, there are plenty of fliers who mix their own APCP rocket motors In the Research Propellant Forum that would likely beat the pants off of any pyrotechnician who’s only used to compressed powder propellants. If it’s compressed BP only allowed then you guys are in for an entertaining bang up affair. . Kurt #### John Ross ##### Active Member Your post in this thread is much appreciated and raises a number of interesting points. I'll try to address them as best I can. Unfortunately, I haven't quite figured out the technique to construct a post that has multiple segments of someone else's post quoted, interspersed with my own commentary, where the quoted parts are visibly distinct from my replies. First of all, understand that I have not yet personally spoken to any of the judges at PGI to clarify what exact criteria they use in judging the "best rocket motor" category. That said, I believe I have a pretty good idea of what they are looking for, and maximum altitude may be a consideration, but I am all but certain that it is not the most important one. Second, competitors in the Rocket category are NOT limited to black powder motors, although I'd say at least half of the competitors use some variant of BP in their entries. Whistle and Strobe rockets are common, and these motors use none of the components found in black powder. Most relevant to your question, the oxidizer in strobe comp is Ammonium Perchlorate, so that chemical (and all others) is allowed in the making of rocket comps. Third, remember that with fireworks, it's all about the visual. The difference between the "Best Rocket" and "Best Rocket Motor" categories is that the former is judged on everything the rocket does, which obviously includes what happens after the motor burns out. That's where we get creative with our headings. The latter category is all about what the motor itself does, and a flash report to provide a visual of the motor's apogee is the only heading permitted. Remember, this is fireworks we're talking about here, and it's all about the visual. I have never seen an HPR launch in person, and certainly not at night, but I doubt that any of your AP composite motors leave a hanging trail of glowing embers, 8 feet in diameter, stretching hundreds of yards into the sky. Last of all, and probably most importantly, PGI rules state very clearly what is allowed to be purchased and not made by the competitor. The relevant part for those in the rocket competition is "cardboard cylinders, tubes, and discs." You can buy high quality, convolute paper tubes that will withstand 10,000 psi pressing pressure on the comp, but the components that (I think) go into a typical HPR motor would be prohibited. On the other hand, if you've got an idea as to how I could build a motor that is similar to one of yours but using a paper tube and a pressed clay nozzle, I'm all ears. You are right when you say that BP motors have more and more issues the bigger they get, and any firework rocket builder worth his salt has had his share of CATOs (Catastrophe At Take Off) or BOAS (Bomb On A Stick.) What most of us do is to find a combination that works reliably, and then launch the motor shortly after building it. For reasons that are not entirely understood, top-performing firework motors that have been pressed and stored, even for a few weeks, can CATO while the same motor, pressed that day or a day or two before, will work fine. The most common explanation, and the one I subscribe to, is the "relaxation theory," where the high quality paper tube, held in a tube support and filled with comp pressed to 10,000 psi, begins to expand internally over time, developing tiny cracks in the pressed composition. The most powerful motors I have made personally use tubes that are 15 inches in length, with a 1.5 inch ID. They use a bit over a pound of comp. I'm attaching a thrust file of one of these that I put on my test stand. This is not the most powerful motor I have ever made, but I feared that a whistle motor of the same size might trash my test cell. Lately I have gotten away from building the 1.5 inch ID motors in favor of those in the relatively uncommon "4 pound" (archaic designation for rockets) size of 1.25 inch. The reason for this is that the tubes are one quarter the cost of the 6 pound size, and 1.25" ID is the maximum allowed in the "medium rocket" category at PGI. Most competitors in this category enter with "3 pound" rockets that have a 1 inch ID. I am attaching a photo of this tube and the spindle I designed for it. It is spiral wound, which is normally a no-no for high-performance rocket motors, but I've had good results from this manufacturer's products. To the right of the spindle is a convolute wound tube 4" long and 1" ID. These are 20 cents each and I use them for development of comps that will be used in larger motors. I can press one of these in about 5 minutes total time, and with Whistle mix, they'll send a 3" ball shell to 300 feet or better. Also attached is a picture of my 25 ton rocket press. I enjoy building and watching firework rockets for all the obvious reasons, but I'll list one more by quoting my friend and mentor Mike Swisher: "Scientific advancement nowadays is almost entirely confined to purpose-designed research labs and people whose entire professional careers involve scientific inquiry, but it wasn't always thus. "Isaac Newton was a math teacher not normally involved in Physics, and his personal interest was in alchemy, of all things. Antoine Levoisier was only a scientist because of personal interest, not profession. He was a tax collector, which was why he was executed by guillotine during the French Revolution. "Today, pyrotechnics is one of the last frontiers of scientific inquiry where advancements are coming from amateurs and not just professional specialists." JR #### Attachments • 513 bytes Views: 3 • 102.1 KB Views: 10 • 84.1 KB Views: 10 Last edited: #### prfesser ##### Lifetime Supporter TRF Lifetime Supporter Remember, this is fireworks we're talking about here, and it's all about the visual. I have never seen an HPR launch in person, and certainly not at night, but I doubt that any of your AP composite motors leave a hanging trail of glowing embers, 8 feet in diameter, stretching hundreds of yards into the sky. You may want to look at "Skidmark", "Metalstorm", "Spitfire" motors. On the other hand, if you've got an idea as to how I could build a motor that is similar to one of yours but using a paper tube and a pressed clay nozzle, I'm all ears. Some amateurs have used nozzles that erode---throat wears away, reducing pressure---along with a coreburning propellant grain that increases in pressure during the burn. When balanced properly, usually by trial and error, it can give a suitable flat-thrust burn. Since APCP is elastic and cures by chemical reaction there should be less difficulty with propellant de-bonding from the case. And as with fireworks BP motors, the flame doesn't contact the case until the end of the burn, so a suitably thick paper tube should work. You are right when you say that BP motors have more and more issues the bigger they get, and any firework rocket builder worth his salt has had his share of CATOs (Catastrophe At Take Off) or BOAS (Bomb On A Stick.) What most of us do is to find a combination that works reliably, and then launch the motor shortly after building it. For reasons that are not entirely understood, top-performing firework motors that have been pressed and stored, even for a few weeks, can CATO while the same motor, pressed that day or a day or two before, will work fine. The most common explanation, and the one I subscribe to, is the "relaxation theory," where the high quality paper tube, held in a tube support and filled with comp pressed to 10,000 psi, begins to expand internally over time, developing tiny cracks in the pressed composition. I've not been at a PGI meeting in some years, but my understanding is that some pyrotechnicians there have made large pressed BP motors using fiberglass casings. If those can perform properly when made in advance, it would be some evidence that your explanation is correct, as fiberglass ought not to yield the way that paper can. Many years back "Silver Streak" high-power BP motors were popular, though they had a regrettable tendency to overpressurize when not ignited properly. The largest one was an H-200 I think, and used a 1.5" o.d. aluminum case about a foot long. Best -- Terry #### ksaves2 ##### Lifetime Supporter TRF Lifetime Supporter Hi, I realize the difference between amateur rocketry and pyrotechnics. I love a great fireworks show. Thanks for the clarification above. Heed what the Prfesser mentions. An APCP sparky motor can be extremely impressive at night and moreso than any loft trail I’ve seen from a pyrotechnic airburst shell. I can’t recall seeing a spark trail as impressive as an APCP sparky motor. Sheesh, these motors are impressive in broad daylight. If I understand correctly “Best Rocket” is important the “show” it puts on after the motor burns out. In that case, I would think a simple electronic timer to acctuate an ematch to activate a modest blowing charge for the display portion of the stack would be sufficient. In fact, if a deployment altimeter were incorporated also, the lofting rocket could be recovered and be reusable. It depends if the PGI rules stipulate a “one way ride” with no large pieces allowed after the rocket and display shell does, well it’s thing. That would be more challenging to pull off. That is have no large descending pieces after display In fact if used, a regular APCP sparky rocket motor for lofting the components, the black smoke could be deleted from the mixture since it’s meant for a night display. The black smoke is used to provide contrast in the daylight when a sparky motor is flown. Makes it more impressive. Afraid though one would have to mix their own APCP sparky without the black smoke producing component as all the commercial motors I think have it. Another issue with a sparky is it has a tendency to beat the daylights out of the nozzle so if it’s an erosive nozzle, it would take experimentation to get it right. That means a lot of trial and error. A graphite nozzled project a large chunk of graphite falling out of the sky wouldn’t be a smart thing for a pyro display. Also if the APCP mix configuration is not quite matched correctly to the nozzle throat ie. too small, an over pressurization of the rocket casing will occur. That is because graphite doesn’t erode much and it’s much more important to get the rocket motor grain geometry correct. The display shell if flown on a CATO loft, could go off in a less than nominal direction if timer based. Orientation is important so the display portion is in the right direction when it is released. Me thinks this would be a very difficult task to pull off. Kurt Savegnago #### John Ross ##### Active Member Thanks for both of your replies. I'll address some of the things both of you mused about in a single post. I'm attaching a screenshot of the PGI rulebook section on rocket competition, with an earlier section on general requirements pasted into it. First, I believe fiberglass motor tubes might be permitted in competition if they had been constructed by the builder himself, and not purchased. I could easily do that as I am competent with fiberglass, having built and flown an experimental aircraft constructed out of it. Aluminum tubes would never be permitted. Regarding the construction of HPR-type motors with graphite nozzles, I'd say that they might be permitted at the PGI, if you could show that the competitor himself had made them, perhaps with a video. I have no idea how to make a graphite nozzle, but I suppose I could learn. Regarding the fear of a graphite nozzle falling out of the sky and being a danger (how heavy are they, anyway?), I will say this: Safety is paramount at the PGI Convention, but the shoot site itself is always laid out in such a way that things falling from the sky present no danger to the participants or spectators. At every convention I've ever been to, someone has had the time fuse on a large ball shell (perhaps 12 inches in diameter and weighing 20 pounds) fail to take fire, and the shell has fallen to earth from an altitude of nearly a quarter mile. The mortars are all angled and the fallout zone laid out in such a way that if this happens, no human is in danger. This is true even in the occasional instance where the time fuse smolders and the ball shell explodes on impact with the ground. Conscientious rocket builders that participate at local club shoots often construct their large rockets with "stick buster" salutes, designed to ignite after the heading goes off and blow the stick off the expended motor, to prevent their spent rockets from falling at high speed towards the ground. At PGI, this is unnecessary because of the aforementioned size and layout of the fallout area. It's also true at my own test site on my property, where all my rockets are launched over the Mississippi River. Regarding Kurt's thoughts about using electronic timers and the like, I am almost certain that such devices would not be permitted by PGI in competition. Even if "constructed" by the rocket builder with a soldering gun, the builder certainly didn't construct the diodes, rectifiers, and other electronic doodads that went into the device. (I throw around these technical terms in complete ignorance, as I have a learning disability when it comes to understanding anything with wires that is more complicated than a single function light switch.) Once again, thanks for the great discussion. JR #### Attachments • 162.8 KB Views: 11 Last edited: #### John Kemker ##### Well-Known Member TRF Supporter <snip> There’s a reason why one doesn’t see F or higher impulse BP motors being commercially made. A lot of trouble for consistency. I don’t think anything higher than a BP ”F” was ever available? Oldsters correct me if I’m wrong. <snip> If it’s simply fly a rocket motor, if APCP is allowed, there are plenty of fliers who mix their own APCP rocket motors In the Research Propellant Forum that would likely beat the pants off of any pyrotechnician who’s only used to compressed powder propellants. If it’s compressed BP only allowed then you guys are in for an entertaining bang up affair. . Kurt Rocketflite had F, G and H BP motors. They utilized an aluminum casing surrounded by a carboard outer wrap for insulation. Coreburners, they were very fast motors. In addition to normal motors, there were "Silver Streak" versions that were some of the first sparkly motors commercially available. Semi-Oldster #### afadeev ##### Well-Known Member TRF Supporter I read with interest the pinned topic on altimeters and GPS units suitable for rocketry. How many of these units are useful in situations where you know in advance that you are not going to be able to retrieve the unit after the flight? There are plenty of reliable commercial GPS transmitter-receiver sets optimized for rocketry. If you are comfortable with soldering, Eggtimer kits are hard to beat on price ($125 for the pair): http://eggtimerrocketry.com/home/eggfinder-gps-tracking-system/
If not interested in soldering, then consider MissleWorks kits ($175+): https://www.missileworks.com/store/#!/T3-GPS-Tracker-System/c/25228124/offset=0&sort=normal I assume there are now units that will send information to a smartphone or pad device in real time, and not depend on physically retrieving the unit after the flight and plugging it into a computer with a USB cable in order to download the data. Are any such units cheap enough for one-time use? You may be conflating GPS trackers and Altimeters in your thinking. Usually, those are two separate systems (though there are a few products that combine the two). GPS trackers do transmit position remotely, usually once a second or so. Altimeters do not transmit the data, but they do sample the data (Timestamp, Altitude, Velocity, Temperature, Events) a lot more frequently (at 20+Hz, or 20+ times per second) , and can trigger deployment charges on demand (e.g.: at apogee, at 500 feet, etc). Most altimeters also store the data in the device (built-in memory, or a removable flash card) for subsequent retrieval and analysis. Most of us find$150-$500 investment in the electronics to be sufficiently meaningful to avoid treating it as one-time use equipment. In other words, if you put$500 worth of electronics into your rocket, a GPS tracker also goes in for the ride so that you can get it all back.

Then there are the \$2+K systems that will do all of the above, plus transmit onboard telemetry, plus talk to you in a sexy voice: https://www.multitronix.com/

There are a lot of us who spend thousands of dollars and hundreds of hours preparing for and attending the annual convention, just as I'm sure it is with you guys in HPR events. Another couple hundred bucks for a fistful of altimeter/GPS units is something I believe a lot of people, especially competitors, would add to their budgets for the PGI convention.
Agreed.