I have the Pro Chrono blue tooth model mentioned above, and it is a very good chronograph. Mine works fine even after putting a bullet through it! But I have been using a Magnetospeed V3 more in recent years. I do a lot of air rifle tuning at home, and it's nice to have a chrono that I can use indoors with no need for light. It operates by using magnetic fields that are embedded in the bayonet unit that attaches to the barrel, so you need minimal space. I usually shoot into a box beside my stool. The only downside, it's a bit cumbersome when working with multiple rifles, since you have to attach the bayonet component to the barrel. It takes only seconds to attach, but you need to first determine the correct spacer, based on the diameter of the barrel or suppressor. It's a great option if you need it indoors.