1. The problem statement, all variables and given/known data Im not sure how to measure the wavelength when given this picture. 2. Relevant equations The picture looks like this, it has two slits. 3. The attempt at a solution My book says that the wavelength is 1 cm. When I measure from the middle of a white line to the middle of the next white line, I get 0.5cm. Same for the black lines. Am I missing something here or isnt that how youre supposed to find the wavelength? Just want to determine if its me or the book thats wrong.