1."I see this item as a tool for evaluating my own designs mostly. I don't see a big market where diver would really want this." Agree
2. "As for the Big boys, making Guns and Pole spears, I'm sure they already have their designs completely tested for this kind of basic stuff."
:thinking: Maybe it is just me not paying attention or it is true that I have yet to see ANY gun / band / spear maker EVER post ANY FPS (feet per second) numbers about their product. I continually read/hear terms like "shoots fast, slow, lots of penetration, accurate, shoots hard", etc. But I cannot ever remember seeing a true FPS written about a speargun shaft speed. Way back in the day before the wheel in archery, we were happy to get 175+FPS from our recurve bows. We didn't REALLY know how fast/slow our arrows were UNTIL we began using arrow chronographs. With the advent of arrow chronographs and the invention of the wheel on archery bows, arrow chronographs have played a HUGE role in arrow speeds and bow design. Arrow speeds have climbed from 150 to 300+fps and there is talk of 400fps designs coming, all with the help of chronographs. IMO, speargun design is much the same as archery bow design, in the context that the stored energy of the archery bow limb and the speargun band function through stored energy to propel the arrow or spear. Granted there are HUGE differences between a 200gr arrow shot through the air and a 60inch SS spear with a string attached shot through the water, but the some same concepts of trajectory, speed, and kinetic energy apply, and a spear chronograph could be a very useful development tool. IMO
Years ago Tin Man wrote about ideas of how to measure spear speed that seemed like a good approach to measuring spear speed. Perhaps his approach could be investigated.