Model of gamma compensated ionisation chamber type RC6, made by 20th Century Electronics in 1967. The ionisation chamber contains two oppositely-charged electrodes arranged so that, when the gas is ionised (ie: by X-rays), the ions are drawn to the electrodes, creating a current. This is used as a measure of the intensity of the ionising radiation. The model was made for, and presented to, Gilbert Tomes by his workforce at 20th Century Electronics (Later Centronic Ltd)