response from manufacturer on accuracy of Dillon D-Terminato

[mitchx3]

Sam: Am I missing something here? (I copied your first 2 columns.)

[Seismic Sam]

Thank you mitch, and we were both missing something, and it was bugging the hell out of me until I figured out the right graphical presentation of the data. It took me four tries to get the graph to show what I wanted.

The statement that the actual grain weight varies from the displayed weight by a maximum of .05 grains is in fact true. That statement, however, carries with it some assumptions that the variability is centered about the actual weight (that is actually true) and the variability is a normal gaussian distribution, which in this case is hideously false, and the BIG lie as far as this data is concerned. So: I did a chart of the variance between actual grain weight (four decimal places, based on the four figure conversion factor of 15.43 grains per gram)) calculated from a gram weight (with a precision of .01 grams) and the displayed grain weight with a precision of 0.1 grains. (1 decimal place)

The graph of the variances is shown below:



OHHHH!!! Bet you weren't expecting that!! (I wasn't either... )

The variance is NOT gaussian, but linear, and much worse that that, it flip-flops from a erroneous high weight to an erroneous low weight with every increase of .01 gram, and then repeats the cycle with every increase of .1 gram. So, at the worst, an increase of .02 gram will take your from a grain weight that is .05 grains high STRAIGHT to one that is .05 grains low!! And let's be clear about the real problem here: You have NO IDEA where you are on this chart with any given powder charge!! Maybe you're going up and down by .01 grains, and maybe you're going up and down by .05 grains, You will NEVER have a clue without a reference balance to check your data, which means this digital balance is NOT reliable.

And consider the most likely scenario for loading up a string of loads over a range of 0.1 grain increments: Chrono data!! You load up ten strings of 5 loads each in .1 grain increments, and you are GUARANTEED that you will cross over one of those up .05 - down .05 transitions. That means that in actuality, you will have TWO 5 shot strings that are the same weight (when they are supposed to be 0.2 grains apart), and they will either be on the high side or the low side, but in any case your chrono data will be thoroughly screwed up.

The WHOLE point of load development and chronoing your loads is to establish a predictable relationship between powder weight and velocity, and with this kind of ramped flip-flop behavior in variance you might as well never even bother to take you gun out of the safe.

So, that extra powder isn't dangerous per se, but it COMPLETELY blocks you from doing any RELIABLE load development work. For THIS you want to pay good money??

[gyrfalcon]

So basically Dillon was lying when they said the scale is accurate to 0.1 grain... They should say it's accurate to +-0.2gr right?

[RAGGED]

So basically Dillon was lying when they said the scale is accurate to 0.1 grain... They should say it's accurate to +-0.2gr right?

They are not alone, this is true of all of them.

[rugersol]

So basically Dillon was lying when they said the scale is accurate to 0.1 grain... They should say it's accurate to +-0.2gr right?

They are not alone, this is true of all of them.

Regarding reloading scales under $140, I've seen no exceptions.

Sam, excellent graph ... Thanks!

[Seismic Sam]

So basically Dillon was lying when they said the scale is accurate to 0.1 grain... They should say it's accurate to +-0.2gr right?

Well, the answer isn't that simple. In a normal discussion of weight accuracy with a digital readout, there are some inherent statistical assumptions that are completely violated by the .01 gram to 0.1 grain conversion with these types of scales. The first is the sad fact that it appears that more often than not, a scale like this is incapable of EVER displaying certain weights in 0.1 grain increments such as 1.3 grains, 1.6 grains, 1.8 grains, 2.1 grains, 2.4 grains, 2.7 grains, etc., etc. In a rational discussion of scale accuracy, there is just NO place for this embarassing fact to fit in. It's as if the grain display was one of those old style "figure 8" led displays with some of the elements burned out. You can't start making statements about the accuracy of a scale this is not functioning properly or is partially broken, so it's simply not appropriate to attach an accuracy range to it.

Secondly, there is the nasty fact that if you do want to cite actual variances, they CHANGE with each different weight value expressed in .01 gram format. Going from the left side of the chart, the +/- weight accuracy in grains is -.045, +.010, -.035, +.015, -.028, +.025, etc. etc. Once again, there is no place in a normal discussion concerning scale accuracy for a variance that flip-flops positive to negative AND changes magnitude with every different weight measured.

So, while it's probably a fact that these digital scales could be characterized by saying that the displayed grain weight is within +/- .2 grains of the true weight, that fails to communicate to the user that more than HALF of the possible grain weights cannot be displayed, and the weight error is jumping around like a jack rabbit with every weight measured.

[1911fan]

Ok, a question, is this a case of software, or of hardware.

Are there scales that are set up to "think" in grains first, which is where I see all the problems arising from is not the physical nature of the scale but in the base software that runs the scale as a gram scale and then does the math to convert.

What would it take to 'reprogram" the scale to think in grains first?

are there any ways to fix this?

[Seismic Sam]

Ok, a question, is this a case of software, or of hardware.

Are there scales that are set up to "think" in grains first, which is where I see all the problems arising from is not the physical nature of the scale but in the base software that runs the scale as a gram scale and then does the math to convert.

What would it take to 'reprogram" the scale to think in grains first?

are there any ways to fix this?

The only way to fix this is to create a gram scale that has an accuracy of .005 gram. If it doesn't have thet sensitivity in grams, then it won't have it in grains even if you do a reprogram. The scale MUST have a sensitivity of .005 gram to be in the ballpark. No tickee, no weighee...

[mitchx3]

Scales initially 'think' in basic electrical terms.

Somewhere an ADC converts electrical numbers to arbitrary numbers that are computed and sent out in some format.

http://en.wikipedia.org/wiki/Strain_gauge

[gyrfalcon]

Somewhere an ADC converts electrical numbers to arbitrary numbers that are computed and sent out in some format.

I agree that it could be correct or mitigated by redesigning or reprogramming the scales. The load cell or transducer in the scale has a certain resolution, and that resolution is not tied to any specific weight system. The companies selling these scales probably bought a pre-designed sensor unit that was setup to measure in grams. This sensor unit may be completely un-upgradable because the transducer and logic for it is built into a small electrical package.

[1911fan]

Somewhere an ADC converts electrical numbers to arbitrary numbers that are computed and sent out in some format.

I agree that it could be correct or mitigated by redesigning or reprogramming the scales. The load cell or transducer in the scale has a certain resolution, and that resolution is not tied to any specific weight system. The companies selling these scales probably bought a pre-designed sensor unit that was setup to measure in grams. This sensor unit may be completely un-upgradable because the transducer and logic for it is built into a small electrical package.

I understand that the scale does not think. What I was trying to get at is you have roughly 454 grams to the pound, and 7000 grains to the pound, by my meager math skills, If a scale was primarily programed to use grains as the base measurement, and then did the math to get the gram weight, it would be a better system for both. Hence I was asking if there were any scales programed to work that way. Any scale which was accurate in its base system to .o1 grains, would inherently be at least .oo5 gram accurate which is .00001101 of a pound, while .01 grain accuracy is .00000143 of a pound.

So again my question are there any reasonable priced scales which use Grains as the base unit of measurement.

[mitchx3]

So again my question are there any reasonable priced scales which use Grains as the base unit of measurement.

Unlikely and hard to verify, but adding 1 or 2 digits to the right of the decimal eliminates this issue.

[jdege]

To repeat what I said above, ANY scale that has an accuracy of .01 grams and 0.1 grains is fundamentally flawed in its precision specification, and shouldn't be trusted for a reloading application.

You just need to shoot bigger guns.

If you're loading .25 ACP, the difference between 1.4 grains and 1.5 grains could matter a lot. In a .50 BMG, the difference between 185.5 and 185.6 grains isn't likely to matter at all.

[Seismic Sam]

To repeat what I said above, ANY scale that has an accuracy of .01 grams and 0.1 grains is fundamentally flawed in its precision specification, and shouldn't be trusted for a reloading application.

You just need to shoot bigger guns.

If you're loading .25 ACP, the difference between 1.4 grains and 1.5 grains could matter a lot. In a .50 BMG, the difference between 185.5 and 185.6 grains isn't likely to matter at all.

Somebody clue jedge in on the caliber of guns I DO shoot!!

[goalie]

You just need to shoot bigger guns.

Oooh, that is funny.