Accurate Static Pulling (with electric motor?)
This is a fairly common thing to do with electric motors. Essentially you need to control the motor's current. The current is proportional to torque using a constant called the torque constant \$K_t\$ with units \$(Nm/A)\$, which is often given in a motors datasheet. If you can control the current flowing into the motor, say using a PI(D) controller then you can fairly accurately know the torque by the following equation \$\tau = iK_t\$.
The accuracy will depend on how you measure the current feedback and how you design your controller. Typically current measurements are fairly noisy so you will need low pass filtering to reject noise before being fed back into your controller.
It is important to note that the torque constant will not always be provided to you on a motor datasheet, and instead you will be presented with another constant known as the back emf constant \$K_e\$. If you convert the back emf constant into units of \$Vs/rad\$ then it will be the same value and the same units as the torque constant.