 An NMR spectrometer typically consists of a spinning sample-holder inside a very strong magnet, a radio-frequency emitter and a receiver with a probe (an antenna assembly) that goes inside the magnet to surround the sample, optionally gradient coils for diffusion measurements, and electronics to control the system.Spinning the sample is usually necessary to average out diffusional motion, however some experiments call for a stationary sample when solution movement is an important variable.For instance, measurements of diffusion constants ("diffusion ordered spectroscopy" or DOSY) are done using a stationary sample with spinning off, and flow cells can be used for online analysis of process flows.