An apparatus is utilized for measuring a circumference. The apparatus includes a body section, and at least one wheel rotatably attached to the body section. Additionally, at least one vacuum generating device is disposed on the body section, and is configured to generate an effective amount of vacuum between the body section and an adjacent arcuate surface which is sufficient to retain the body section against the arcuate surface. At least one of a reflector and a gap detector may also be affixed to the body section.