Definition of spectrometer. 1  1 : an instrument used for measuring wavelengths of light spectra. 2  2 : any of various analytical instruments in which an emission (as of particles or radiation) is dispersed according to some property (as mass or energy) of the emission and the amount of dispersion is measured nuclear magnetic resonance spectrometer.
1 bar is equal to 1000 millibars. Just like how there are 1000 millilitres in a litre, and 1000 milliseconds in a second. 1 millibar = 0.001 bars.
Since the measurement is in the metric system, 1,000 millibars equal one bar. A bar is a force of 100,000 Newtons acting on a square meter, which is too large of a unit to be a convenient measure of Earth's air pressure. Inches of mercury and centimeters of mercury measure how high the pressure pushes the mercury in a barometer. (Related: Calculate pressure conversions).