Correct measurement is extremely important. Therefore, calibration of components of the instrument is needed. The general characteristics of measuring equipment are described. Two general groups of measurement devices are described. The primary measurement device for dose is the ionization chamber and its connection via cable to the electrometer. The types of electrometers are described. The other major devices used are solid-state devices, either luminescent or electrical, which are described. A brief introduction to this category of devices is given.