The In-Plane Laser Vibrometer is designed to measure the velocity of a surface moving in a plane perpendicular to the bisector of the two converging laser probes. The frequency shift (Doppler Effect) of the back-scattered laser light is used to determine the velocity. Non contact, load-free velocity measurement is essential to study and develop tape drives, ultrasonic knives and scalpels, photocopiers, printers, belt drives and other moving parts where slippage, vibration and mass-loading can be a problem.