To zero a reading out on the meter, press the REL button; this subtracts the value from the displayed number. It stores that value in the event it is desired to bring that value back into the number that was measured. An example may be the resistance in the set of test leads being used. It may have a minor value that is not critical in some larger measurements, but in small measurements starting from zero may be necessary in certain applications. The value can be toggled with the current signal and back again if desired.