I bought an expensive RCBS Range Master digital scale. It's accurate. Here is how I know:
When I first tried the LEE Pro Auto-Disk Powder measure, I set it up to throw 4.9 grains of Unique powder using hole size .53 as per the directions. But according to my LEE Safety Powder Scale, it was way under 4.0 grains. So I tried the next higher up (.57) and still way under, then tried the next (.61) and STILL too low! Using the 3 holes away (6.6) gave me about 5.1 grains.
Obviously there was something wrong with the cheap little LEE balance scale. No way would LEE offer directions for their powder measure that are so ridiculously low, they could result in a squib and be dangerous. Right?
So I went out and bought an expensive RCBS. It measured EXACTLY the same as the LEE Safety Scale. So that's how I know the RCBS is accurate. What a friggin waste of money.
Oh well, I guess I have a backup in case the RCBS breaks.