The SI unit for speed is m/s, but science often uses other units for the sake of convenience. Magnetic tape speeds are often measured in in/s, and vehicle speed in mph or km/h. The speeds of spacecraft are often measured in km/s, mps, or as a Mach number (Mach 1=340.3 m/s) and of very slow event (such as glaciers) in units like m/year. Some reciprocal units (used e.g. in running) are also available in the units menu.