First, it is necessary to have the input divider calibrated. After switching on the oscilloscope, wait 3 minutes, perform base calibration. And after turn on ONE channels of DC mod and measurement, bring a suitable signal to input. (eg rectangle or sine 5V peak to peak and 2.5V offset), press auto button. The option "dc shift calibration" is activated in the diagnostic menu. In the oscilloscope mode, the CTRL key is pressed. The menu to the right allows you to change the value of dc_shift_center, place the signal in the center. (You can check whether the signal is in the center using the cursors.)
The default value is 112, decreasing the value moves the signal up, increasing the value moves the signal down.
Change the value, press the CTRL button, press AUTOSET, the change of signal location will be reflected. If the signal is not placed symmetrically on the central axis. Repeat the whole process.
Then disconnect the signal from the oscilloscope!!!
With a value of 2, set the straight signal line to coincide with the channel cursor.
With a value of 3, set so that the value of Vmin = 0mV
Press end cal.
The option "dc shift calibration" deactivated in the diagnostic menu.