To put it all together -

You can guarantee that with a stepper motor any STEP will be within 3 to 5% accuracy when it stops ( and it is only on that step) - so if you have 200 step per rev, the accuracy of the stop is 5/20,000 of a full rev or 0.09 of a degree if my maths is right.

The accuracy of the micro steps cannot be guaranteed, but even if they were twice as large since there are 8 to make up a step, it must be still more accurate that a full step.

The only time it comes to bite you is if you are relying on this in your computation of steps per unit.

Mine is geared down, and I need 48,000 steps per inch. So I need 48 steps per thousanth of an inch so I can get very accurate (if I can manage 1/2 a thou I will be happy, so I have 24 steps to play with).

If I geared up my axis drive for speed - say direct motors and much more pitch on the leadscrew - took out the 3 to 1 reduction and altered the leadscrew to say 1/2 pitch (a bit excessive, but you get the idea) then I would be down to 8,000 steps per inch - only 8 steps per thousanth of an inch.

Still enough for me, you might say, but in the quest for speed (some talk of 100 inches per minute) these ratios might increase until you were is a position when microsteps start coming into the calculations of standard units of mm or inch. If, say, you got down to 5 microsteps per thousanth then you cannot guarantee the accuracy as you can with a full step.

A lot of time spent discussing a very small difference - since it is non-cumulative - but neither can it be calculated.

It all depends on what you want your machine for - if you are working in wood clearly any accuracy you decide on does not really matter, because wood expands and contracts dependent on humidity. Some plastics do the same with temperature.

I work mainly with steel and would like to be able to guarantee 1/2 a thou on my parts (I can't measure any better anyway) - so I am on 48,000 steps per inch - my movement (if you followed the other thread) I have settled at 12 inches per minute, which is comfortably within the capablilities of my motors - without taking too long to move about.

It all depends what you want - accuracy or speed.