I am getting readings on my chrony that are 100 fps lower than published data. Sometimes more. Using same bullet, powder,primer and barrel length(257 WB). I contacted Chrony and they insisted that the unit does not need to be calibrated except every 10 years if that. Does anyone know of a test method for a chronograph? When this first happened the shells had been sitting in the cold and it was not extreme powder. Hogdon said you can get anywhere from a 200-400 fps variation from 0-125 degrees F With some of there powders. I was around 250fps low. It was around "0" ,and the shells had been sitting in the cold, so I chalked that up to the temp. I shot some more of the same load in the spring and it was better but only by 1/2. I also have a 280 Rem and that has been right at 100 fps off on the publised data. Nosler did say that the test barrels they use produce higher velocities. Do match grade barrels produce hight velocities? I have been kicking around the idea of getting another chrony and mounting them inline to check each other. Any one do this or do you just trust the chony?