Hello. So, I am building a camera and have ran into a problem that I feel could be solved with a semi-simple function. There is a reel-to-reel system for winding the film from a spool to a dowel of 3/4 inch diameter. I need to know how many turns of this dowel would result in advancing the film a certain distance. I could find the circumference and multiply that by number of turns, but as the circumference increases each turn, this would prove inaccurate after the dozens of turns it would take to reach the end of the reel. I am asking for a function that takes the number of times turned (or rather which turn it is, to avoid a zero) and outputs the number of turns next needed to advance the film a constant amount. Thank you.