The outputs of each operational amplifier is input into a subtracter circuit to subtract common dark or photocurrent components so the output of the subtracter circuit is proportional to {HEAD ~ the difference} in {TAIL ~ light incident} on the photodiodes 
in
The outputs of each operational amplifier is input into a subtracter circuit to subtract common dark or photocurrent components so the output of the subtracter circuit is proportional to { HEAD ~ the difference } in { TAIL ~ light incident } on the photodiodes
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH