I found it pretty accurate for my 10XL in my Revo but not so with my XL3100. With my XL3100 it was doing over 50mph easy on 12 cells but the calculator said 32....20mph off is a big difference. Whereas, it said 42 for my 10XL which is about right. Why was it off so much on the Lehner motor but not the Feigao?