A correction signal is applied to {HEAD ~ the modulator} to maintain {TAIL ~ substantially uniform exposure} across the output medium notwithstanding variations in the velocity of the beam 
to maintain
A correction signal is applied to { HEAD ~ the modulator } to maintain { TAIL ~ substantially uniform exposure } across the output medium notwithstanding variations in the velocity of the beam
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH