Have you ever had thoughts to build your own motor driven mount? Then you need to know how to get the gear ratios you need. You also need to know what angular resolution your motor works with, what does one step from your motor correspond to in arc seconds.
I have made a Mount Gear Ratios calculator on my homepage. It's new for today and there can be some mathematical erros in the calculation so double check everything before you buy any expensive parts!
Here it is:
Let me know if you find anything wrong with it.