Use Pythagoras. Let Pen tip = P. We know L1, L2, X1. Define line segments R1 -> P = L1, R1 -> x = A, (x,0) -> P = B. A2 + B2 = L12 We know the length of A is X, since it's (0,0) -> (x,0), and we know length of B is y, since it's (x,0) to (x,y) x2 + y2 = L12 Let R2 -> P = L2, x -> R2 = C B2 + C2 = L22 A + C = X1 => C = X1 - A So we have x2 + y2 = L12 y2 + (X1 - x)2 = L22 Solve these and you get x and y
cheers Chris Maunder