Subclass 3/16: Measuring distances in line of sight; Optical rangefinders (tapes, chains, or wheels for measuring length G01B 3/00; active triangulation systems, i.e. using the transmission and reflection of electromagnetic waves other than radio waves, G01S 17/48) using a parallactic triangle with variable angles and a base of fixed length in the observation station, e.g. in the instrument with binocular observation at a single point, e.g. stereoscopic type (G01C 3/2 takes precedence) Measuring marks