This paper examines the use of speciallized silicon detectors in position and angle measurement systems. The operational characteristics of segmented position sensors are compared with those of lateral cell position sensors. Segmented position sensors of the quadrant and bi-cell variety exhibit the greater position sensitivity and resolution but have dynamic operating ranges which are limited to the dimensions of the optical image focused onto the detector. Segmented cells require uniform illumination intensity in the spot to achieve good linearity. They can operate at bandwidths of well over 100 megahertz as may be required in pulsed and high-speed tracking applications. Lateral cells are available in single and dual axis con-figurations. Their dynamic operating range is independent of spot size (excluding edge obscuration effects). Linearity and absolute measurement accuracy is also independent of spot size and uniformity characteristics to first order. Other advantages include excellent linearity, large operating range, and electronically adjustable null. Angle, x-y displacement and z-axis measuring schemes are discussed and two in-process measuring systems using lateral cells are described: an electronic auto-collimator for measuring tappet bore angles and an automatic "seam tracker" used to guide a TIG welding head.