(m) The SI base unit of distance.
Definition: 1983 defined as the distance traveled by light in a vacuum during the time interval of 1/299 792 458 of a second.
The speed of light in a vacuum, c, is one of the fundamental constants of nature.

1 meter (m) is equal to approximately 39.370 079 inches (in)
1 meter is equal to approximately 3.280 840 feet (ft)
1 meter is equal to approximately 1.093 613 3 yard (yd)
1 square meter (m²) is equal to approximately 10.763911 square feet (ft²)
1 inch = 2.54 centimeters
Smaller or larger units are, e.g.:
1 meter (m) = 1 000 millimeter (mm)
1 micrometer (µm) = 10^-6 meter (m)
1 nanometer (nm) = 10^-9 meter (m)
1 picometer (pm) = 10^-12 meter (m)
1 femtometer (fm) = 10^-15 meter (m)
1 kilometer (km) = 1 000 meter (m)
1 kilometer (km) = 0.62137 (statute) miles (mi)

See also System International.

A densitometer (also called absorptiometer) is used to measure the density of a film by the amount of light which shines through; or tissue density (e.g., bone, lung) by the amount of radiation transmission. The logarithm of the reciprocal of the transmittance is called the absorbance or density.

A pulse oximeter is a medical device that displays a digital percentage readout of a calculated value of the hemoglobin that is saturated with oxygen (SpO2).

A radiation meter is used to measure radioactivity.
Beta emitting isotopes, such as C-14, P-32, P-33, and S-35, are best detected with a Geiger-Mueller counter (GM).
Gamma emitting isotopes, such as I-125, I-123, I-131, and Tc-99m are easily detected with a gamma meter equipped with a sodium iodide (NaI) probe.
An isotope that cannot be detected with most survey meters, unless present in large activities, is tritium (H-3). Tritium emits beta particles with energies insufficient to enter the sensitive volume of most detectors.

(TLD) A thermoluminescent dosimeter contains a crystalline material (lithium fluoride, phosphor) for measuring radiation dose. TLDs are usually small crystals measuring 3 mm square by 1 mm thickness. Additional filters (absorbers) help to characterize the types of the impinging radiation. When heated, TLD crystals that have been exposed to ionizing radiation give off light proportional to the received energy.