Using convergence tape for measuring rock movement in a tunnel during construction to control the stability of the excavation is a common practice. In this technique a number of reference points (convergence pins) are installed around the tunnel periphery. After each face advance, the distance between pairs of pins is measured by 0.01 mm accuracy. Stability of the tunnel can then be evaluated according to the recorded deformations. Usually in this method, the exact locations of pins after deformations are not determined and just changes in length are measured. In this paper, methods of calculating exact coordinates of pins are presented by using convergence tape as the main instrument and leveling tools and single point extensometers as complementary. Recommendations are also made to optimize the  installation location of the pins to maximize obtained information from the readings and ease of interpretations. In the second part of the paper, error sources in Sakurai’s formula for back analysis of tunnel deformation is detected and eliminated by using the offered generalized formula.