To measure plant growth rate. The recording arm 600 mm with a bristle tip at one end is mounted on an adjustable pillar enabling alteration of height and pressure of the bristle on a disc of 200 mm dia. The other end of the arm has three eyes to give x3, x4, x5 magnifications. A smoked disc is mounted on a circular plate which is clamped to a motor spindle, & has a central pin to prevent the lever passing the center. The disc rotates at a speed of one revolution per hour.