CoreFree
mAs and reciprocity
mAs = mA × seconds. Any mA and time that give the same mAs give the same receptor exposure.
What it measures
mAs is milliamperes multiplied by exposure time in seconds. mA sets how many electrons cross the tube each second, and time sets how many seconds they flow, so mAs is the total number of electrons, and with it the total number of x-ray photons produced. Double the mAs and you double the photons, the receptor exposure and the patient dose. mAs controls the quantity of the beam, not its energy; that is kVp's job.