The components of Beer’s Law can be determined by tests. They can also be referenced in literature. If the absorption is measured by a UV-visible spectrophotometer (instrument to measure absorption and wavelength of molecules), pathlength (b) is related to the sample container used in the test. The sample container (named a cuvette) is made of a material that does not absorb light in this region. The thickness of this cuvette is a known value. This is the pathlength the light will travel through to reach the sample. 