rear differential, rear differential, rear wheels

I cant read the build code (to worn ) to see gear ratio on 93 Yukon rear diff. Any other way to determine this?  

Answer
    They used to put a little tag on one of the bolts that holds the cover on, but they don't do that anymore.  Jack both rear wheels off the ground and put them on jack stands.  Put the trans in neutral.  Then have two friends turn the rear wheels exactly one full turn, keeping them in sync or close.  While they do that, count the number of turns of the pinion (where the rear u-joint attaches).  That gives you your ratio.  If the wheels turn once and the pinion turns 2-3/4 times, it's 2.73.  If the the pinion turns three and a half turns, it's 3.56.  Pretty simple, actually, and lots better than hoping you got the codes right.  If it's four-wheel drive the front ratio will be the same, of course.  Another option would be to take the cover off and count the teeth on the sprocket and pinion, then divide.  This is even better, but much messier.
Car Repair Talk's forum.