Reply #19: This is what Washburn has to say about the accuracy of scales.

[eridani]

This money will buy a counting scale with a capacity of 50 to 70 pounds and a sensitivity of 0.005 pounds (2 grams). A single 8.5”x11” sheet of 80 pound card-stock weighs 8 grams. A ballot printed on heavier card stock or on a larger size would weigh more. Thus the ballot is well above the readability of the scale and is able to distinguish differences of even a single ballot.

I have a ream of 80 lb stock. I'll check out the variability of the weights and estimate the error when I have time.