Put the axle up on a pair of jackstands.
Turn the pinion shaft in one direction while a helper watches both axle hubs.
If they turn in opposite directions from one another , it's an open diff.
Now set the pinion yoke with a bearing cup at 12 o'clock , mark it at the top with a sharpie pen.
Without moving the pinion , mark an axle hub at 12 o'clock.
With your helper watching the hub , count the turns of the pinion it takes for the hub to make exactly one revolution.
Just a tad over 4 revs = 4.10
3 and 3/4 revs = 3.73
Those are the most common.
Archimedes screwed us !
I knew a blonde dyslexic agnostic insomniac - she'd lay awake at night, wondering if there really was a Dog.
2003 Ranger Edge 3.0 manual 2WD