Most non-goto equatorial mounts have setting circles-- marked circles that show the right ascension and declination at which the scope is pointed. You can use these circles to locate objects (provided you know their RA and Dec), but they require setup-- you have to have an accurate polar alignment, and then you have to make sure the circles themselves are properly set. And you need circles large enough to be readable with reasonable accuracy.
Digital Setting Circles came along after computers got small and cheap enough. They were a common add-on to equatorial fork mounted SCTs (with tracking motors) for a while. With the DSC, you could get greater accuracy for the RA/Dec location, and the computer could have the coordinates of popular targets. And as the Dob revolution took off, the DSC idea was adapted to work with Alt-Az coordinates.
The big difference between DSCs and goto is that a non-Goto DSC scope does not have automated slewing to the target. The DSC computer tells you which way to move the optical tube, but it can't move it for you. For this reason, DSC scopes are sometimes called "push-to" scopes.
The advantages of a push-to scope over a goto is as follows:
- lower cost
- quieter operation
- Quicker moves, provided the operator knows where the objects are
Of course, to achieve the above, you have to give up the scope slewing to an object for you.
You add encoders to your RA and declination axes and