The number of gear teeth between {HEAD ~ adjacent bulged regions} differs between the two gears and {TAIL ~ the relative motion} between the two gears is caused by shifting of the engagement regions 
The number of gear teeth between { HEAD ~ adjacent bulged regions } differs between the two gears and { TAIL ~ the relative motion } between the two gears is caused by shifting of the engagement regions
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH