IIRC, when I did the arithmetic years and years ago, each tooth was worth ~ 1.67%. Which meant you should be able to get it within 1% either way +/- if your speedo head is working correctly. FWIW, YMMV, ect. 2¢

Roibert

'68 Fury Convertible
'69 300 Convertible
'15 Durango 5.7 Hemi
'16 300 S Hemi