Interesting. My ProChronos have rarely missed a shot, and when they did it was my fault, usually for not replacing the battery in time. How old is yours?
Usually have one or two spare batteries with me when I use the chronograph. Sun is pretty intense here in SE Colorado, even with the diffusers on I get errors. It usually works pretty well if I tape a a target to both diffusers, but the if the wind picks up it can become a sail.
Anyway it's not a right now have to purchase.
