In no-load state, the rated current is applied to the winding of a motor by a specified excitation method in order to rotate a rotor one step at a time from any point on the rotor as the starting point.
The differences between the theoretical positions and the actual positions of the rotor for each step are measured over the entire circumference.
After that, reverse the moving direction and measure the difference toward the original starting point.
The half of the maximum difference between the positive and negative values including hysteresis is called the positional accuracy.
("Glossary and definition for stepping motors" by Japan Electrical Manufacturers' Association.")