How to get joint torque by joint current?

Hi,
I basically have the same question.
I found this thread Some doubts about URScript: get_tcp_foce - URScript - Universal Robots Forum (universal-robots.com).
However, the proposed method of dividing target moments by target current does not yield constants at all. So I would also like to know how the script function computes the torque. Is it based on some nonlinear motor model?