There is (or was) a test stand on the market that had a thrust measuring device on it, but I haven't seen it advertised in a while. Probably among the combat/racing/speed guys. The measuremenys you get with a make-shift rig will be suspect for real accuracy, but at least you can get some comparison data. BTW, have you experimented with props on your trainer? A prop change can make all the difference in the world.