Bell Prover : A device used for testing the accuracy of gas meters, consisting of a sealed 'bell' to or from which a measurable amount of a test gas (usually air) may be passed
Ministry of Business, Innovation and Employment, Glossary of terms and acronyms, Wellington, New Zealand 2010. http://wwwsosh.govt.nz/resources/glossary-u.shtml, (Occupn Hlth and Sfty - Brit) {530}