I have learned to tune up my scale (a RCBS 10-10). I removed the agate pieces that the beam knife edges rest on and cleaned them and the metal that touches them with alcohol and Q tips. After replacing them, I leveled the base of the scale, removed the pan holder, disassembled it, removed one of the spherical weights, reassembled it, and assembled the scale, with the weight and adjustment set to 0 and the pan in place. I then started adding small pieces of plastic (snipped from a spare shirt collar stay) to the scale pan, until an exact zero was reached (using the mirror technique explained above). I then took the pan holder apart and added the plastic pieces to the collection of spherical weights, and reassembled the pan holder and the scale. It was right back on zero. Next I checked it against some check weights, and it came out right on the money. I keep the dust cover on the scale, except when it is being used, and store it in its original cardboard box, in a drawer. I might add that I have tuned up three scales of the same make and model that had previously had to have their left ends jacked up well past level to zero the scale. I think that this puts the Vs in the agates in misalignment with the beam knife edges, resulting is poor performance. They all worked much better after the tune-up.
