The direction of bed offset across a fault is a function of four angular variables. Any fault may have a unique combination of the four variables yielding a null combination at which there is no bed offset regardless of the amount of net slip. Furthermore, a given fault movement can cause bed offset in either direction depending on the null combination, even if only dip-slip movement is involved. Consequently, the upthrown or downthrown side of a dip-slip fault commonly cannot be determined positively from outcrop pattern alone, and the absence of certain strata in a vertical borehole does not necessarily indicate a normal fault.