Do your probes have a X1/X10 switch on them?
It looks to me as though the blue trace (channel A) has a X10 probe attached, so that the sensitivity is really 10 x 2V = 20V per division.
If the yellow trace has a X1 probe attached, then the sensitivity would be 10V per division (as indicated).
That would explain why the yellow trace is roughly twice as large as the blue trace.
There is a manual for the DS203 oscilloscope here.
(I think it's the same as yours).