Help with gear ratio when engine/transm. removed

[Lee Mitch]

I am trying to determine the differential gear ratio and need a little help. My engine and transmission are removed and I was wondering how I could calculate the ratio by watching the driveshaft turn in comparison to the rear tires. I was assuming that I could watch the shaft turn 2 complete revolutions and watch how much the rear tires rotate (like you do with the engine turning 2 complete revolutions) and I would have my answer. I was figuring that in that configuration I would be in 3rd/direct drive. Obviously I am incorrect. Any help out there? Thanks in advance