Wavelength meters are devices that measure the wavelength of electromagnetic waves. They are typically bench or desktop mounted, and provide a numeral value of pulsed and continuous-wave lasers. They are more accurate that a spectrometer of grating monochromator and can have very low tolerances--as little as hundredths of a picometer. They typically consist of a photosensor, amplifiers, a thermostat, and interferometers, as well as software and a user interface.