I'm a little new to reloading and I want to do everything right but I'm having trouble with my powder scales. I have an older RCBS (not sure of model), a Lee safety scale and a cheap Hornady digital and I like the RCBS best for ease of use but both my beam scales have the same problem.
The problem is that when I zero them they will settle out for a second then start jumping around again. They will also do the same thing when I try to weigh a powder charge. I've tried them in different rooms thinking I was getting some kind of weird electrical interference or air flow from the ceiling fan but got the same results. I've also cleaned the scales and inspected them really well and can't find anything wrong visually.
Is there anything I can do to fix this problem or am I doing something wrong?

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