Metrology
The dial is only a calibration. What the instrument actually measures is how much swing the pendulum lost.
— N
From the energy the pendulum lost to the tear
Frictionless pendulum with all lost energy attributed to the tear. A real instrument loses some to bearing friction and air, which is exactly what the no-specimen zero swing is for — subtract that loss before trusting an absolute figure.
Elmendorf Pendulum Energy & Tear Force Calculator — free, with the formula and a worked example, at Textile School.