Oh my goodness, how cool is that. I love the way you showed clearly exactly what you were doing. Poor old Bob, I hope he wasn't hurt in his trampoline experiment. Thanks so muh for the vid. It is brilliant and congrats on your homemade stretcher.
That video has been posted several times here in the last few years and yes it does work as I have tried it. I built mine on a table though and instead of a screw to test the tension I use a tension meter. I am a fan of the DIY so I try them all and this method does work.