For some strange reason about 10 years ago I decided I wanted to collect some of the legacy balance beam scales when they were all over Ebay. I ended up with about eight scales that went back over 30 years or so. The ones with the all brass beam and weights were really nice when cleaned up a little bit.
Long story short, using a set of check weights all of the scales were within 1/10 grain accuracy even after all those years. Might be an argument that gravity is constant as long as you are on the same place on earth. Regardless of the brand of the scales, Ohaus made most of the ones I was able to collect. Made in USA and used USA gravity to function
None of the digital scales I have used (all under $75.00) have ever given me as consistent readings as the balance beam.
If I want to weigh powder I use a balance beam.
If I want to separate case or bullet weights I use a digital. Relative as opposed to accurate is the key in this case.