This type works by the projectile making a shadow above two sensors. When the projectile passes over one sensor a timer is started. when it goes over the second sensor that stops the timer. You need good lighting for this type of chronograph, but Chrony is still the industry standard. I use the light inside because of the fluorescent lighting. Fluorescent lighting flickers faster than we can dream of shooting, but to us appears to be constant. This can play hell if you are trying to capture the shadow of something the size of a bb on a photo sensor. That's why I run the light kit. I tried to make my own light kit using two 1 watt Cree LED's so I wouldn't have to run an extension cord. It didn't work, and since I ordered the light kit also I just went to that. If you are outside on a bright sunny day you shouldn't have a problem, but you will probably want to use the diffuser's anyway. Be sure you don't buy the model for archery. The Beta model will let you save ten round strings to review later. Since I film most of my tests I really don't need this feature, but it is nice to have the remote display that can be detached from the Chrony. You may want to have someone who speaks Canadian to translate the owner's manual for you.
