I'm cheap... I made my incidence meter. Amazing how EASY it is... (and for under $3 I have an incidence meter and a control deflection guage and a balancing stand for my models... scrap rods, dowels, clothespins and kid's 3rd grade style protractors and just a little bit of thinking...)

The Robart incidence meter is mechanical... and if it isn't vertical... it may bind a little. Its no big deal and may not be a problem with the meter. The dihedral of the model may have you holding the meter at a small angle that is causing the binding. Tilt the meter so its straight up and down and the weighted part should swing freely again.