My brother has an archery pro shop, and a professional, large ,expensive, chrony. It is big ,and red. Don't know the name of it, but it is a professional model. Big bucks. My brothers ,and I have the red chronies like above. On any given day cloudy, sunny, or in between when we check ours against his which we do often some days the readings are spot on. Other days up to 5fps difference, but I have never seen 15 to 20 fps.