I think pretty much under a 100 mph they are real close but once you get over a 100 mph they start being a little less accurate. Still close but off by 4-10 mph depending on speed. My friends 800 ski doo says he is going 125+ mph. And he totally believed it. And I told him no way was it that fast. Well he argued and argued until we found a good stretch and I put my phone in his pocket and he took off. Well he came back saying 125 mph then he looked and my phone said 102mph. So he was pissed and didn't believe my phone and still claims his stock 800 power tec sled does 125. Lol... I told him he is crazy. I could beat him with my Nytro and he drove my Nytro and it said 114 on the speedo and he still says his can do 125. Lmao it makes me laugh just writing this.