Weapons analysis readout displaying CpM
Counts per minute (abbrev. CpM, or more accurately Cpm) was a measurement used to determine the amount of ion radiation was present. Such a measurement could be determination by an ion trace scan.
The weapons analysis made by Malcolm Reed of the the debris of a Rigelian freighter that was discovered by Enterprise in late 2154 determined that the amount of ion radiation in the area was 569 CpM. This was one of the indicators that confirmed a Klingon weapon signature. (ENT: "Affliction" display readout)