Chronographs in paintball are used to check the velocity of paintball guns so that you can set them to a safe velocity. ASTM rules state below 300 feet per second is the safe playing speed for paintball fields in the USA. Most paintball fields usually have a top speed of 285 because CO2 can flucuate by 15 degrees easily throughout the day. Using compressed air or nitrogen will make your paintball gun a lot more consistent over CO2. There are a few types of chronographs available on the market so choose the right one for you. You have your small hand held units which are great for refferees to have on the field or to check your speeds at home. The other chronos are great to use for paintball fields.