An optic fiber strain measurement sensing mechanism has been developed that can measure extremely low strains, i.e. in the order of 0-25 microstrains, with a resolution close to 0.1 microstrain. It is an alternate to traditional foil gauges as well as the more recent Fabry-Perot sensors for some applications. It is particularly suited to measure very low strains in large scale infrastructures where portions of the infrastructure can be used to mount extended lengths of the fiber optic, thereby providing high resolution. Examples of such applications are the measurement of small strains or vibrations in large structures such as rocket test stands, buildings, oil rigs, bridges, dams, etc. The sensing system includes all off-the-shelf components and the focus of this paper is to provide details on how to develop the system, calibrate it and then use it for specific applications. © 2008 Elsevier Ltd.