Tape extensometer is designed to take accurate distance measurements between pairs of reference points permanently installed. The instrument is a removable stainless steel measuring tape with equally spaced punched holes incorporated in a lightweight alluminium body with external pneumatic tensioning device (compressor) and dial gauge. Portable compressor provides the same tension to the tape during measurements, which permits accurate readings. Typical applications include convergence monitoring of tunnel linings, according to NATM practise, and of shafts, underground openings and caverns.