One turn or two turns?

[marty in Ohio]

I'm trying to determine the gear ratio in my '30 town sedan. I removed the plugs, jacked up one wheel and marked it at the 6 o'clock position, and put the transmission in 3rd gear. I turned the engine over with the crank two times (like it was described to me a year ago on Ford Barn) and the tire mark ended up in the 5 o'clock position. When I tried again and only turned the crank one revolution the tire mark ended up between the 11 and 12 o'clock position. What am I doing wrong? One wheel up - two turns on the crank - third gear.