Rigol DS2072 math A-B doesn’t work. Others okay

[Circlotron]

Firmware 00.03.05.SP3
Hardware version 2.
I want to use differential input mode so channel 1 normal and invert channel 2 and use math A-B function. Purple line is flat no matter how far up the sensitivity is wound. Other simple arithmetic functions appear to be okay.

Anyone else see this?

[texaspyro]

I want to use differential input mode so channel 1 normal and invert channel 2 and use math A-B function. Purple line is flat no matter how far up the sensitivity is wound. Other simple arithmetic functions appear to be okay.

ch1 - (-ch2) would display ch1+ch2.  I don't think you want to invert channel 2 for a differential display  if you are using an (A-B) math function.

[Circlotron]

I tried every combination of normal and inverting of both channels but still no cigar.

[JDubU]

I also have a DS2072 with hardware version 2 and firmware v00.03.05.SP3.

I connected both probes to the scope's square wave calibration output lug with channel 2 set to invert.
Here is a screenshot using Math A-B.  Note that Source A and Source B need to be set in the math controls

[Circlotron]

Note that Source A and Source B need to be set in the math controls

That was it. Both sources were set as Ch1. The tricky part was that AxB, A/B and A+B all still give a reading of sorts so I never thought of that. What's more, I have only ever used the advanced option, and with that you type in an equation that has the choices of Ch2 and Ch2. You don't have to assign them as such.