Forget the marks and counting while turning stuff. Use a long piece of masking tape to tape some string to the drive-shaft. Place the tape parallel to the length of the shaft with one end of the string under the end closest to the trans and the other end of the string laying on the ground. With both rear tires off the ground turn one tire a full revolution. Count how many full & partial times the string crosses over the tape. E.G. if it crosses the string twice and gets about 3/4 of a revolution then the ratio is about 2.75:1; if it crosses the string 4 times plus about 1/2 of turn then the ratio is likely 4.56:1
