Digital phase-shifting photoelasticity 1)2) can be regarded as an extension of recently introduced computer-aided phase-shifting methods, the objective of which is the detection of one phase (e.g. 3)4)), to a two-phase problem. The two phases governing, in a general case, intensity distributions of photo-elastic patterns of planely stressed bodies are: relative retardation S(xl,x2), which is related to the difference of local principal stresses, and isoclinic parameter a(x1,x2), which describes the angular position of local principal axes belonging to principal stresses ai ?ooli. It is known from photoelastic point methods (compensation and ac-phase measurement techniques5)) that phase-shifting of photoelastic patterns is achieved by independent rotation of two polarizing components of a polariscope.