So far as a power calculation no, I wont release my formula to people but I am happy to run a maths channel on VBOX .vbo or .dbn (perf box) files, these cheaper ones are inexpensive really and are
the testing standard ........... everyone should own one
Never any dispute with information you record off one of these instruments.
Some of the other vendors equivalent 10hz GPS add on's are a joke when you look at the update rate and quality of speed trace they give, I would not trust them personally.
The VBOX (Performance box branded) ghetto units I have tested parallel to my old VBOX III and also my new VBOX 3i and they are bang on .......... it's what you want mate.