I use this one. Itworks perfect anfd gives you two settings for the chance that you have two sets of tires (snow/mudders). I have seen several others that were cheaper. I think in Summit racings catalog has a 'Jet' brand, not sure though. Just keep googling it in different ways. i just googled 'speed calibrator' and a full page of choices came up. Use a portable GPS to set the speed right on. By the way, I used to live in Mesa and then in Chandler before moving to the country of Texas.