It is super simple.You have two options.On the speedo healer site you can eitheir do the exact or estimate tune.The exact is meant to use if you have actually used a GPS to determine what speed you are going compared to the speed that your speedo indicates after the chain and sporcket change.The estimate lets you throw in what changes you have made(sprocket size,ect...) and other factors such as tire wear.Once you decide a method to use punch in the numbers and press calculate and it gives you step by step instructions.Trust me guys im no math mathecian(or speller for that matter) and i figured it out.And know compared to the HSCO speed indicators mine is pretty much dead on..Hope this helps!