Hi, I ordered a radarchron because it sounded portable and handy. Noticed the plus or minus spec but figured I wouldn't mind just shooting a string of shots, say 10, and averaging them to get a fairly accurate number. Also figured I would chrony my bow at a shop to see what the diff was, and could adjust the radarchron the percentage and be fine. What happened was I discovered the radarchron was 1 fps off the shop chrony, and it was consistently plus or minus about 1 fps readout. In other words, it was virtually perfect. Haven't fooled with it with other bows, and think it may need to be adjusted height wise to read correctly on diff bows. To be fair I have read of others who have had the same experience as me, and some who claim awful results. Don't know how to explain that. But I love mine. Thought I would let you know what I experienced.