stepper motor accuracy

Hi list,

Trying to figure out what is involved in determining the accuracy of
a stepper motor.

Some extracts from Gecko's "ACCURACY AND RESOLUTION" for stepper
motors.

Finally, the static or frictional load applied to the motor affects
accuracy. A stopped step motor, which has 100 oz/in of holding
torque, is fundamentally different than a break that has the same
holding torque.

The break will not turn at all until its holding torque is exceed.
However a step motor only generates restoring torque if it is
displaced from its rest position Using the brake analogy, think of
the output shaft being connected to the break with a torsional
spring. Now when applying a load, the output shaft has to be radially
displaced to apply torque to the break.

When torque sufficient to overcome the holding torque is applied to a
step motor, the shaft will jump to the next stable location, which is
4 full steps ahead or behind the original one, depending on which
direction the load is applied. Peak restoring torque occurs a full
step ahead or behind the original location, beyond which it weakens
and reverses at the 2 full step ahead position to attract the shaft
to a full step location ahead or behind the original one.

QUESTION:
What is "a break that has the same holding torque"?
http://www.denford.com/
What is the above trying to explain?

What relevance has the above to, say, a step motor controlling the
movement of the x-axis of a milling machine? The torque mentioned
above originate from where in this milling machine - the frictional
force that prevent the tool from moving in the x-direction or the
turning force from the current applied to the coils of the stepper
motor?

Thanks

Pal