# question about altimeters

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#### rocketsonly

##### Well-Known Member
Has anyone used the Perfectflite Alt15k/WD altimeter (no deployment)? Have you all noticed how sometimes the altimeter will read the same altitude when the rocket is traveling upwards? And sometimes a reading may be higher than the previous reading when coming down?

Is this normal for all altimeters or is it just the Alt15k/WD altimeter? Do the BlackSky altimeters do the same thing?

Any feedback would be greatly appreciated .

Thanks.

#### llickteig1

##### KLOUDBusters Chief Logistician
I am not sure what you're trying to ask.

Is you observation during groung testing, read from the download or what?

You might drop a mail to PerfectFlite with your question. I have always had their products perform as expected and I own MAWD and Alt15k/WD.

--Lance.

------

Also, consider losing the red background on the rocketguts website. Marketing people will tell you red is bad. That may or may not be true, but it definitely makes rocketguts.com visually unpleasant to visit.

#### solrules

##### Well-Known Member
I know that the Perfectflite MAWD altimeters do something like that. The Ozark Aerospace ARTS does the same thing as well. From this, I would imagine that it happens with all altimeters. I guess the altimeter is sampling the barometric sensor faster than it can change, errors in the 12 A2D converter, or something else.

When the rocket is going down, a small wind gust could push more air into the sensor, making it think it is lower than it actually is.

Here is what he is talking about (for example)

Code:
TIME        ALT

2.05        1000
2.1          1000
2.15        1000
2.2          1025
2.25        1025

#### rocketsonly

##### Well-Known Member
Originally posted by solrules
I know that the Perfectflite MAWD altimeters do something like that. The Ozark Aerospace ARTS does the same thing as well. From this, I would imagine that it happens with all altimeters. I guess the altimeter is sampling the barometric sensor faster than it can change, errors in the 12 A2D converter, or something else.

When the rocket is going down, a small wind gust could push more air into the sensor, making it think it is lower than it actually is.

Here is what he is talking about (for example)

Code:
TIME        ALT

2.05        1000
2.1          1000
2.15        1000
2.2          1025
2.25        1025
Yup, that's what I meant. I'll see what Perfectflite has to say.

#### Hospital_Rocket

##### Well-Known Member
The owners of PerfectFlite are members of CATO and I pinged them outside the forum to see if they can help you out.

A

#### cls

##### Well-Known Member
my perfectflite MAWD and 15k both do that, as do both the baro and the accell on both of my GWiz MCs. none of these are accurate to the foot or meter, I'd be surprised if they were within 15 meters or 50 feet.

the stepping up in numbers has to do with sampling rate (how often the computer is reading the instrument), and the resolution of the measurement. google for Nyquist and see what he has to say about it.