edit: while writing this question, I found out one way of doing it so I figured I'll write it up for future reference and anyone else having the same question
thanks for some really great hard-/software!
I'm currently measuring the power consumption of a low-power device (milliwatt range) by measuring the voltage drop over a 10 ohm high-precision resistor in series with the power supply to the device. Nothing fancy, all standard stuff. However, I would like Picoscope to calculate the power consumption of a part of my sampled waveform (eg over 1 second of time, how much power is consumed?). With math channels I can integrate easily but only (?) over the entire trace. How can I choose a subset of the trace and integrate over it?
the solution I found was adding a measurement of 'DC average', from "Choose what section..." chose 'between rulers'. Then from the bottom left corner of the sampling window there will be a small white box that you can drag into the window. Do it twice to define the rulers between where to measure. Read out the DC average in the small measurement box in the bottom.