Home Forums Hunting & Shooting Ask The Gunwriters Digital Scale vs. Balance

Been doing some tests on the Lyman digital scale (which is quite a nice unit, by the way), vs. my old faithful Hornady reloading balance. Thought you guys might enjoy some numbers.

Background: Practically all measurement systems have some random error in them. This is the limiting factor for most measurement systems. It defines the smallest difference you can resolve, and any attempt to calibrate to something finer than that is futile.

The figure of merit is sigmaE, the standard deviation of the random error. Smaller is better.

Results: SigmaE for the digital scale is .1 grain, vs. .043 for the balance. So 95% of the time, the digital scale is within plus or minus .2 grains of the average you would get with many, many weighings of the same object. For the balance, 95% of readings will fall within plus or minus .086 grain.

In a 30-06, .2 grains corresponds with ROUGHLY 6 degrees F of rifle temperature, so it isn't much to worry about. Bottom line is that both devices are probably quite adequate.

Denton how did you determine the smallest resolution? Both types scales are normally advertized to be accurate to +/- 0.10 grain. To be this accurate I would have thought they would both be capable of 0.050 grain resolution or better.

Interesting though, I wonder if other reloading scale brands follow suit with these findings.

The procedure is to get a couple of dozen test objects (in this case pieces of gravel), and to measure each of them twice. The difference between the first and second measuring is caused by measurement system error, and you can derive the sigmaE from a pile of those differences.

Effective Resolution is .67*sigmaE, so the digital scale has quite a good resolution, and the balance a little better. You can kinda eyeball .05 grain on a balance, so you can get better than .1 grain repeatability. I seriously doubt that absolute accuracy is that good. And it doesn't matter... it's plenty good.

A few years ago I looked into an electronic scale, but decided against it because the manufacturer (RCBS in this case) said that its accuracy would be affected by ambient temperature. Since my reloading area's temperature fluctuates seasonally between about 40 F and 100 F, I stayed with the balance. Do you have any measurements under different ambient temperatures for both the electronic scale and balance? I'd be interested if you do.

chinook...

With any luck, I'll take that data today, for both devices.

I have both, and like them.
But I do want to say thanks for taking the time to do this and informing us of the results.
We do appreciated the info offered by the many that do these tests.

chinook...

Did the "temperature torture test" this afternoon. Here is the short version of the results.

Took both units directly to a 53 F shop from a warm house. The digital scale would not accept the calibration command until the shop and unit warmed to 71 F. This was probably because the temperature was changing too fast, not because it was cold.

Once the digital scale would calibrate, it produced results indistinguishable from the indoor test done earlier. The manual is probably overly pessimistic when it says to let it stabilize for 24 hours. An hour seems to work fine.

For the balance I started at 53, and did measurements while the shop warmed over a period of a couple of hours (numerous breaks to do other things). An electric heater was running, which creates air currents. After half the measurements were done, I turned off the heat, and opened the doors, which created more air currents, and did the rest of the measurements as the shop cooled. I tore the balance down five times during the test, and re-assembled and re-zeroed it. In short, I gave it every chance to fail. Result: Practically identical with the stable warm test earlier. Balance completely unfazed.

The rest of the story will be in an upcoming issue of Varmint Hunter.

Thanks for taking this on. I hated to part with that digital scale. But, my old RCBS balance has been so reliable, and I've successfully loaded so many rounds with it, that it just made me feel more confident to keep using it.

Thanks again.

Denton, while you are testing scales, have you ever noticed the phases of the moon changing the zero on your balance beams? I have an old RCBS 304 that has been my main scale but it does seem to shift zero ever so slightly over the months time. One might think it's just the age of the scale but it has been that way since new.

Thanks,
Max

Denton: In my own experience, there is a fairly large source of error (at least plus or minus 0.1 grain, maybe more) in the balance scales arising from the slight variations in the way in which the powder is distributed in the bottom of the pan. (I don't have any experience with digital scales so I can't speak to whether the same thing causes variations in those scales.) These differences in the way in which the powder is distributed can be so slight that they are not readily visually apparent to the user; yet they can still result in more than plus or minus 0.1 grain in the measurement. The important thing is that if you are weighing pieces of gravel, your tests will not produce the same kind of variations that you would have gotten if you had used powder in the tests. Would you want to try the same test using powder rather than gravel? I think that you would get different results if you did, and the results of that test would be more realistic for the uses to which we are putting these scales.

BigBrass

That's a very good suggestion. Thank you.

Denton...

When you say "balance" I assume you mean a caliberated scale that is read by the human eye on markings put on some field by a machine controlled by humans. The MAIN difference is the reading of the human eye on the markings made by humans rather than the analog numbers produced by the digital scale.

I think the difference is in the human eye's abiltiy to detect differences in the readings. Its hard to mistake a digital scale's reading of 60.0 grains even if you need coke bottle glasses to perceive it. Whats the difference in the width of the lines on a balance? .2 grains? .02 grains? If I line up the lines to the best of my eye's ability am I exact every time to equal that of the digital scale?

The balance scale has V notches for three sliding masses, moving in 10, 1, and .1 grain increments. You get better than .1 grain resolution because next to the pointer at the tip of the beam, there is a scale with marks in .1 grain increments above and below null. You can easily tell when the pointer falls between two marks. This gives the balance scale the ability to resolve differences smaller than .1 grain. Testing confirms that the real resolution is on the order of .03 grain, though absolute accuracy probably isn't nearly that good.

OTH, in the couple of hundred balance measurements I made, I misread the scale three times, vs. 0 on the digital scale.

Denton, dont forget paralax! Unless your scales are on eye level. Besides I trust my brain better reading real numbers than setting all the little aluminum slides just so. Im simple that way! Hey, what can I say, Im a lawyer...brain good with abstracts....concrete things really confound me! <img src="/ubbthreads/images/graemlins/help.gif" alt="" /> They gotta be REALLY concrete or I get confused!