I use this formula: V=1.944xL/T for almost 2 years, it's very accurate. The real speed is when AoB is 90° but as targets move slowly, the error on the speed is very small and you can get a good estimation with AoB 40° or more(if AoB is 0 you can't find a value for speed!). For fast targets it works but you have to be careful and you don't have much time to do this!!
