Megger DCM1500 Guia Del Usuario página 6

Zero
Using the Relative mode (REL), a stable value can be stored, the instrument
zeroed at that point, and then any variation from that value is displayed as
a direct measurement relative to the stable value.
2.
3.
1.
Data Hold
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Make a measurement and then press the ZERO button.
REL: Meter stores the measured value after pressing the
ZERO button.
REL (flashing): The meter saves the offset value. Present
value is displayed.
Normal: Press and hold ZERO for > 2 seconds to return
to normal operation and cancel the offset value.