any possibility for calibration without powermeter

[michal.fm]

Hello,
is there any option to precisely calibrate Rampa without powermeter? I mean if you have (or plan to add for example to my e-training app) some option like spin-down calibration. I guess, for people which do not have PM would be very usefull.
I am using Rampa with my winter bike which has not standard 26x1,25 inch pressurized just to 4 Bar (Hutchinson top slick 2). I have serious doubts that It might influence the accuracy of the trainer. Thanks Michal