a transaction printer includes the micr encoding of indicia at a precise location called the amount field . in order to accomplish this , an optical sensor is provided in a check processing machine at a point - of - sale to detect the edge of the check and stage it at a known location from the thermal , micr print head . a clutch mechanism is used to engage the print head with a platen and to engage a read head with the check , so that indicia can be sequentially imprinted and read within the check processing machine in a single , sequential operation that moves the check from a home position to a micr print position , and subsequently to a micr read position .