Probably because you are using micro-stepping, which gives angular steps much finer than the standard 1.8 degrees but at the expense of torque, which is reduced considerably.
Also, I think Holding Torque is normally higher than Driving Torque. In other words, if the load was equal to the holding torque when stationary, it is possible that it would be unable to step it onward from that position.
Jeff[quote=“matthewepler, post:21, topic:40”]
For accurate reading, should the motor be attached or not?
I would have thought not, if you are just reading the torque to pull the film.