That equation is bogus IF it defines “headshell angle”= headshell offset angle. In which case the skating force would be a constant which we know it is not. However, if headshell angle is defined as (tracking angle error + headshell offset angle), maybe it makes sense. Gotta think about it a little more but that seems to work.
I was interested in your response re how you use the scale. Dover explained your method, or as I understood his explanation of your method, as one in which you hold the scale vertically against the fingerlift on the headshell, with VTF set to zero and the arm floating. From your last post, I gather that is not the case. So what is your method, exactly? Did you try anything akin to my idea?