TRM intern Alvaro Gonzalez Hernandez and his dog Txoki explain the maths behind involutes – the curve formed when a dog unwraps its lead from around a tree trunk. Involutes have been studied throughout history, most notably by Christian Huygens when trying to construct an accurate clock using a pendulum. They are also found in gear systems where the shape of the gears follows that of a circular involute to reduce friction and increase torque.