depends on the distance between the nuclei. Unlike spin-spin coupling, NOE propagates through space and does not require that the atoms are connected by bonds, so it is a true distance measurement instead of a chemical measurement. Unlike diffraction measurements, NOESY does not require a crystalline sample, but is done in solution state and can be applied to substances that are difficult to crystallize. Astronomical distance measurement Other systems of units In some systems of units, unlike the current SI system, lengths are fundamental units (for example, wavelengths in the older SI units and bohrs in atomic units) and are not defined by times of transit. Even in such units, however, the comparison of two lengths can be made by comparing the two transit times of light along the lengths. Such time-of-flight methodology may or may not be more accurate than the determination of a length as a multiple of the fundamental length unit. List of devices Contact devices Architect's scale Caliper Diagonal scale Engineer's scale Feeler gauge,used in metal working to measure size of gaps Gauge blocks Gunter's chain Measuring rod Meter stick Metric scale Micrometer Opisometer or curvimeter Pacing (surveying) Ruler Stadimeter Surveyor's wheel Tape measure Thread pitch gauge Ultrasonic thickness gauge Yard stick Non-contact devices Ranging Based on time-of-flight Electronic distance meter Ultrasonic ranging module (sonar, echo sounding) Radar distance measurement Laser rangefinder, lidar See also Distance-based road exit numbers Linear referencing Meridian arc Milestone Rangefinder GPS, indirect by runtime measurement of electromagnetic waves in the GHz-range Hypsometer Interferometer Macrometer Odometer Position sensor Positioning system Standard ruler, in astronomy Tachymeter Taximeter, measure usually includes a time component as well Tellurometer Travelling microscope Angular measuring instrument Altimeter, height Distance measuring equipment (aviation) Ellipsometry#Imaging ellipsometry Frequency-modulated continuous-wave radar (FMCW) Length scale Low-energy electron microscopy Orders of magnitude (length) Pulse-Doppler radar Range ambiguity resolution Cosmic distance ladder Bradley A. Fiske Dazzle camouflage Depression range finder Fire-control system Range-finder painting Rangefinding telemeter Slant range Tacheometry Telemeter chronograph Tellurometer References Further reading SI units Metrology Scientific techniques Length, distance, or range measuring devices