The voltage at {TAIL ~ the function} of D1 and {HEAD ~ Q1} is a square wave 
The voltage at { TAIL ~ the function } of D1 and { HEAD ~ Q1 } is a square wave
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH