Just a suggestion....one turn of the wheel will make it difficult to accurately determine the ratio. Jack up both wheels. Try turning the wheel 10 times while counting the driveshaft revolutions. Divide the number of d/s revs by 10 and you should have the number.
I've found it's just as easy to pop the cover and read the ratio and other pertinent info off the outer edge of the ring gear. A bit messy but the numbers are stamped, easy to read and eliminate any guesstimates. BTW...if both wheels turn the same direction you've scored a posi diff.
