1. The problem statement, all variables and given/known data Hi Guys, I am a bit confused concerning one part of this topic. Specifically when trying to find non dimensional groups. My problem is a small thing in the finding of the indices. So, for example, your are trying to find a pi group when finding the drag on a car. so you have D,A,V,rho. then you find indices by doing [M][L][T]^-2 ([L]^2)^a ..... and then do [L]: 0 = 1 + 2a... but sometimes I have seen in solution people doing [L]: 1 = 2a... This obviously gives a different answer to the one above. as a = 1/2 for the bottom one and -1/2 for the other. Im confused about which one we are supposed to use for what 2. Relevant equations 3. The attempt at a solution One thing I am finding is that often when it is like [L]: 1= 2a.. that is because the pi group has been labelled D = kA^aV^b rho^c or something like that while then it looks like [L]: 0 = 1 + 2a... it is normall labeled DA^aV^b rho^c. Im not sure what the difference is but the two methods give different numbers and I'm not sure when one should be used or not. I'm not sure why k is in the group above and isn't in the one below etc.. All I am tyring to do is form a functional relationship with things. Thanks, I'm sorry if this is a bit disjointed Im struggling to explain it! I would really appreciate someone setting me straight.