I just started using Picoscope, with Win 98 to parallel port. Using latest software.
Displaying the output of an ac power supply which reads 13.5 V rms (i.e.approx 19V pk) on a meter I get a display (with a 10x probe) of +20V peak to -45V peak. Exactly the same display with connections reversed.
With an AAA cell I get 1.87V with normal connection, and -26.77V reversed.
Also with a half cycle of the 60Hz there seems only to be about 8 samples. It jumps from the zero-crossing to about half amplitude in a straight line although there seem to be more points around the peak.
(I checked the parallel port after reading a previous post and it is set at Normal, 378H and IRQ 7)