I used to teach college chemistry, hence the question of BOTH accuracy AND precision.

Here is a good example everyone here can relate to. You shoot at a target 3 times with 5 different guns.

The 1st gun hits the target low left 1st shot but is off the rings. 2nd shot is high right on the 2 ring. Third shot is off target. This gun is not precise, nor accurate.

The 2nd gun shoots a 4 inch triangular group, high right. It is not precise, nor accurate. Note that it is accurate to the groups mean.

The 3rd gun only hits the 5 ring three times, 120 degrees apart around the X, but the group average is dead on X. This gun is not precise but is accurate.

The 4th gun also hits the 4 ring, all shots nearly in the same hole. This gun is not accurate, but is very precise. Note that is also very accurate to the groups mean.

The 5th gun hits the X all three times. It is BOTH accurate and precise, and accurate to the groups mean.

For firearms it is easy to adjust a precise gun (guns 4 and 5). You adjust the sights to zero. Guns 2 and 3 will never be precise but can be adjusted for accuracy. Gun 1 has problems sighting in/calibrating won't help

So.......back to original question concerning scales.

The OHAS/RCBS 304 balance in working order is a VERY precise scale for reloading, it's accuracy depends on calibration with accurate check weights (weights are accurate or not, no precision involved).

Concerning using coins as check weights. In the past I found the mass of nickels to be BOTH precise and accurate. That is repeatable mass on an analytical balance with say 10 different nickels, AND accurate as each nickel was +/- 0.0002g of the average.

The above was part of an exercise in freshman chemistry. Student weighed coins, steel shot, and beans. Then reported on accuracy and precision for each group of 10.

The nickels were precise and accurate, the beans were neither.

This was years ago and don't have uncirculated 197? nickels handy.