1. The problem statement, all variables and given/known data http://i.imgur.com/xrba7.png 2. Relevant equations I'm using this equation to find the thickness of the polymer. [(m+(1/2)) λ = 2nt] (where "n" is the index of refraction and "t" is the thickness ) 3. The attempt at a solution I just want to know how m is determined. I've learned everything else, but I missed the first day on which m value to use and it's always jsut slipped my mind whenever I'm in class or lab. Thank you for your time.