You can tell the difference by looking at the back of the unit where the RED, BLUE, GREEN... bnc cables come into the unit. A TSKI unit only has a single db9 plug there. A RSKI unit will have 4 ports there, however only 2 of them will be used. 

The RSKI added the ability the run the analog feedrate and spindle override pots through the monitor instead of an ADC board in the I/O rack. Some divisions of Cincinnati used this functionality. If you are not using the analog pot interface on the side of the RSKI board, a TSKI unit will work fine in your machine. Look at the left hand side of the monitor when viewed from the back. You may have to remove the aluminum cover on the side, and see if any wires are hooked to the green or orange connector. If so, you have to have a RSKI unit. 

When you send your OSA in to us to get updated, we like to know what kind of unit we are getting ahead of time so we are prepared.

RSKI:Note the orange connector for pots.

TSKI: No connector for pots

Keyboards:

 There are also 2 types of keyboards Cincinnati used on these controls. The original ones were very low profile. The keys didn't stick up very far past the plasitc bezel. They are a very high quality keyboard, but completely unrepairable. The backing plate of the keyboard was actually made out of aluminum, with a steel cover on the front side of the physical keyboard itself.

The new style keyboards stuck up higher. The key switches are replaceable if you can find them.

 The old style keyboards require some extra machine work on the faceplate to make them work in our monitor. Again, we like to know if they are coming ahead of time.

 New Style:

Old Style: