Shure Stylus Gauge

My theory would be that there is something causing mechanical resistance at the arm bearing as the headshell goes lower. This would explain both the different readings with and without an LP, and also the fact that the arm stays down when pushed down.

There could be a few reasons for this:

First, is your arm mounted at the right height at the pivot? The bearing will only allow the arm to swing free within a certain range.

Second, does your arm have two separate balancing mechanisms, ie, a gross mechanism to get the arm to balance (0 weight) and a second calibrated one to set the actual weight? If so, you should always calibrate the the arm to zero before using your scale. If not, the arm may not be within a range in which the counterweight and stylus force are linear with respect to eachother.

Third, is the tonearm lift interfering?

Fourth, there is some friction at the pivot of the scale (good news) or some friction at the tonearm bearing (bad news).

Hope this helps.

How can I tell if it is the arm bearing. Is there a test I can do? When I set the counter weight to float the arm, it seems to float, and bob up and down, side to side without hesitation at all.

the bearings might do ok but the pivoting position plays the vast role in this situation. the cartridge weight oght to be the same whether you place mat record or none of these. certainly the readings on the soft mat might not be pricese anywhay.