Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter.
A centimetre (international spelling) or centimeter (American spelling) (SI symbol cm) is a unit of length in the metric system, equal to one hundredth of a metre, centi being the SI prefix for a factor of 1/100. The centimetre was the base unit of length in the now deprecated centimetre-gram-second (CGS) system of units.
Though for many physical quantities, SI prefixes for factors of 103--like milli- and kilo---are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an average adult person.
in maps, centimetres are used to make conversions from map scale to real world scale (kilometres)
to represent second moment of areas (cm4)
as the inverse of the Kayser, a CGS unit, and thus a non-SI metric unit of wavenumber: 1 kayser = 1 wave per centimetre; or, more generally, (wavenumber in kaysers) = 1/(wavelength in centimetres). The SI unit of wavenumber is the inverse metre, m-1.