Here's a suggestion - what about reverse calibrating the dial -
Set the VTF to 1.75g using the dial.
Now adjust the counterweight so that the VTF is actually 1.75g at the stylus tip - using your scales.
Now check 1.5g & 2.0g using the dial and scales to see if it is accurate enough to rely on.
Personally I prefer to set VTF with a combination of static and dynamic VTF. A ratio of 2:1 works very well - for example if you want 1.5g tracking force - set static downforce using counterweight to 1.0g and then spring force of 0.5g to bring it up to 1.5g.
This is recommended by Grado after conducting tests - and JCarr also has found a mix of static & dynamic to be optimum.