I went back and found a post I made about a month ago and I have pasted it below. It was hidden under another topic and had no replies. I think it fits into this post along with some of the comments found here.
I hope it is of some interest to someone.
Thanks for such a great forum!
I just unpacked my Lyman balance scales model D-7. It's 20 yr. old but little use and was well packed in original box. I think it's same as Lyman 500 now, it is a 505 gr. scale.
Problem.........When I pulled it from the box, I noticed a very tiny piece of lead that looks like the very tip of a 1/8" twist drill hole. This piece was a calibration weight from the large sliding weight (Poise) on the beam. The back of this lg. weight (Poise) has drill holes in it and I guess they used lead to refil the holes to calibrate it.
Not having any certified weights to check the calibration, I took several cast and jacketed bullets of many sizes and did a weight averaging chart and several calculations. The scales are not right based on my test. I tried putting the tiny weight on the top of the lg. poise and still it was not perfect and noticible up around 400 gr. I could glue the tiny weight back in the hole, but I figure the glue is perhaps enough to throw it off.
Problem is, the heavier your weight, the higher % the scale is off.
I checked with Lyman and about 20 bucks to recalibrate. Add in shipping and ...insurance, 2 ways transportation out and back and I have nearly invested equal to a new scale.
I will buy another new scale and use it to calibrade my old one. For almost the same money as a repair I hope to have two working units.
My point is.......be careful, your balance beam scales could be missing a counter weight so small you would not know it. I think my tiny piece weighed about 4.3 gr. Perhaps I am over cautious but I like to have as much percision as my tools (and budget) will allow.
Maybe someone else has had to recalibrate and can suggest a simple way to double check our scales.