Every person while taking lobster (or other invertebrates that have a minimum size limit) shall carry a device that is capable of accurately measuring the size of the lobster. Due to the curvature of the lobster's carapace (body shell) and the need to measure the lobster in a straight line on the midline of the back, a tape measure or ruler is not capable of measuring the size of the lobster accurately; a gauge with a fixed span works best.