Assuming you mean for train view. There is only support for calibrating Computrainers.
Slope/Zero offset is a feature we could (should?) add for ANT+.
I took a brief look at the code and it looks like the SRM support covers offset and slope, but not for other devices. Thats mostly because I have SRMs :)
It shouldn't be that difficult to complete and expand -- even to incorporate sending the calibration request messages.
I looked and was surprised to see no existing feature request .. do you want to add it?
Mark