I was taught to use effective angle, versus mechanical angle. You set the front wheels straight ahead, then rotate the steering wheel 360 degrees. Effective angle is the degree change of both front wheels, summed, divided by two. Divide the 360 number by the averaged wheel angle change to get your result.
Your Ackerman angles will cause the front wheels to change angle unevenly (side to side compared). If the Ackerman is wrong, you will see that problem by checking ratio results at 90, 180, 270 degree points. Checking effective angles at those multiple data points can be a real eye opener.
You will see that ratio number is a continual change, from straight ahead to full lock...whatever is available.
I really prefer checking this on alignment turn plates, as opposed to measuring wheel rim angle change. Your car only cares about what the wheel to ground interaction does. The initial turn plate line is marked, and the dgree changes are measured on the turn plate, not the wheel. Talk to a local aliignment shop about using or getting their help with a pair of turn plates off the alignment rack.
Hope this helps.
JimL