Long-Slit Acquisition
1) Take an image of the slit position (no grating).
1a) Determine center of slit and position along spatial direction to use.
2) Take two offset images and subtract 1st from 2nd.
3) Locate source on 2nd image and calculate offset to desired slit position.
4) Repeat procedure to insure proper alignment.

Unknowns/Issues: Will the slit reinsert in the same position -- this is important because
(A) the slit needs to be removed and reinserted in order to acquire a target, and
(B) if it is reliable enough the slit position could be measured only at the beginning of the night.

Slit-Mask Acquisition
1) Take an image with the slit mask in.
2) Take second image offset by larger than the slit hole size.
3) Use the second image to determine the center of the holes.
4) Subtract the 2nd image from the first and locate sources. Centroid and calculate offsets.
5) Iterate to insure proper alignment?

Unknowns/Issues: What magnitudes of sources to use/exposure lengths?
How large do the holes need to be/how good is the MMT guiding?