The operation, application, and work-ing theory of an ultra stable laser as a length digitizer is summarized. The two projects presently under way, a 1.6 KM (1 mile) long laser earth strain seis-mometer and a 1-cm pendulum tilt meter, each with a range of 10-12 to 10-5 strain units and radians (or acceleration g units), respectively, are detailed as examples of application. Concepts in angular measurement and servo-controlled physical dimension are reviewed. The perfection of ultra stable lasers has opened the door for a host of even more precise electro-optical mensuration applica-tions. Compact lasers whose absolute frequency stability is measured in kilohertz make possible in practice the use of digital techniques and heterodyne of optical frequencies. This in turn allows the engineering of a "length" digitizer with dynamic range and precision many orders of magnitude beyond the presently accepted state of the art. A dynamic measurement system of dimension of very small (1 cm) to very large (1 km) sized objects is presently under way using this technology. In each case the target recision is 1 in 1012 in dimension and 109:1 in instantaneous dynamic range. The combination of both sensitivity and range represents an advance in the state of the art by about a factor of 104.