Dosimeters come in several varieties. For regular use, staff have a film badge. For high-radiation areas, or for temporary use such as by a visitor, a pencil dosimeter is used. This is like a miniature gold-leaf electroscope. An insulated pin with a metal pointer on a spring is charged up to a high voltage. The static charge causes the pointer to be electrically repelled from the pin. The deflection of the pointer may be read against a scale when the doismeter is held up to the light. Radiation entering the dosimeter ionizes the gas inside, causing it to become conducting and discharging the static charge on the pin. Movement of the pointer away from its maximum deflection is thus a measure of radiation dose.
Your dosimeter will be read by TRIUMF staff before being issued to you, and again when you leave. You can read it yourself at any time.
Ideally, your dosimeter should be clipped to your clothing at vest-pocket level. The radiation dose tables are calibrated using a 'phantom' with a detector in this position.