This app features a mathematical experiment known as the Buffon needle. It is a classic problem of geometric probability, where a needle is dropped randomly in a region of uniformly spaced parallel lines. This app simulates a simple case where the needle length is the distance between two adjacent parallel lines. Let N be the total number of needles thrown at a given time; let C be the number of needles crossing the lines. Let R = 2 × N ÷ C. R is an approximation of Pi ( π). In this app, the user can change the number of needles dropped at each tap and the number of threads in the target region.