GW Instek GDM-398 - Manual (Page 46)

MEASUREMENT OPERATION
44
The Use of Relative Value Mode
The REL mode applies to all measurement functions except frequency/duty cycle
measurement. It subtracts a stored value from the present measurement value and
displays the result.
For instance, if the stored value is 20.0V and the present measurement value is
22.0V, the reading would be 2.0V. If a new measurement value is equal to the
stored value then the reading would be 0.0V.
To enter or exit REL mode:
 Press REL to enter REL mode, and the present measurement is locked as the
stored value. “0” is then shown on the display.
 Press REL again to reset the stored value and exit REL mode.