Diff Identification

[Jonmurgie]

Where are the markings on a diff to show what ratio it is?

I've picked up a second hand one alegedly from an '88 M3 for my M3 and I'm not 100% sure what the ratio is and guess some of the many markings on the outer case must mean something?!

TIA
Jon

[AlexMc]

There is a small metal tag on it underneat one of the bolts.. if it is missing, then mark the output shafts and turn the pinion over until the mark comes full circle. make sure you count how any revolutions it takes! also, on the tag "s" indicates LSD, but again, turn one of the output shafts.. if the other side turns the same direction its an LSD, if it turns backwards its open.