Hi,
* please confirm that your current probe is able to measure DC currents. (Current probe setup and scope setup)
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* Each of the two voltage probes measure the voltage with respect to the GND clip. Therefore you need to connect both GND clips to the same reference point. I recommend to use your circuit GND.
* Both channels need to be set in "DC" mode.
* I recommend to select the same channel_gain for both channels.
* Then use "math" function "Ch2-Ch1"
Klaus