Question On Reading Scales

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11bravo

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I have an RCBS 10-10 reloading scale that I have been using for rocketry.
It is capable of reading out to 1010 grains which equals out to 2.3086 ounces or 65.4469 grams; 7,000 grains = 1 pound.

I attached a Paint drawing that pretty closly resembles what I have and replicates the functionality.

To read it, after twiddling it to get it leveled out, first get the 100's and 10's values from the course setting on the left side, in this case set to 220 grains.
On the right side the grey thing with horizontal black lines and numbers that increase as they go down is a cylinder that you rotate and it moves left or right on the threaded axle that it is on.
It is read by counting how many lines left of 0 the vertical black line towards the left end of it is; use this number as the ones value.
The 10ths are determined by subtracting 0.1 from the lowest number with it's line exposed; in this case 0.6 - 0.1 = 0.5.

The instructions say that a user can measure down to 1/10th of a grain or 1/70,000th of a pound.
However I seem to remember when learning how to use scientific instruments that the user is allowed to estimate to one decimal point between "gradiation marks".

Do I remember correctly?
Or am I having a brain fart?

In the attached, can I only read it to 200 + 7 + 0.5 for a total of 227.5, or can I interpolate between the 0.5 and 0.6 and say that it is really close to halfway and call it 227.55?
IIRC, I can go with the 227.55.

Sorry if the explanation as to how to read it was unnecessary, but I'm sure there are one or two here that have not used something like this and may not be able to understand it.

Thanks,

Greg
 
reasonable.

there's not much point in weighing to the nearest .01 grain unless you are doing quantitative analytical chemistry.

:D
 
Originally posted by Elapid
there's not much point in weighing to the nearest .01 grain unless you are doing quantitative analytical chemistry.

:D

Maybe not, but just to say that you were able to get the weight to the nearest 1 / 700,000th of a pound is quite impressive if you ask me. :D
'Course, I may just be being anal about it. :eek:

Greg
 
Well technically you can only report weights up to the stated accuracy of the scale. For instance, at work I can have the scales display grams out to the thousandth. Doesn't really do me any good as the scales are only calibrated and standardized to the hundreth of a gram. So two decimal places is all I can record unless I want quality to throw a fit. This is what happens when you work in a GMP lab and have the FDA looking over your shoulder.
 
So do you round or truncate?

ie., is 1.237 called 1.23 or 1.24?


If it is 1.24 you are still using the thousandths place.

Greg
 
Yes but you are not reporting the thousandth place. There is a difference.

To answer your question, the scale rounds it. We don't use the .001 g range. The max capacity in that range is too low and we'd need different standardizing weights. Basically the balance is capable of another decimal place but we don't have the need or equipment to calibrate it to that level.

Generally you are right, when reading a scientific instrument such as a graduated cylinder or calipers or a three beam balance you can estimate between graduations. Whether or not your powder scale falls into that category I couldn't say but I think that by taking weights out another decimal place you may cross into where the scale tolerances make it useless. It doesn't do any good to report a weight of 1.237g if the balance is only accurate to .01 +- .005g (tolerances on my small work balance). The actual weight could be 1.232-1.242 g or 1.23-1.24 g. In other words both are right but by convention we round.
 
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