In ductile shear zones, an originally straight marker (like a dyke) crossing the zone is progressively rotated and sheared into a sigmoidal/deflected trace within the zone. The sense of deflection (whether the marker appears offset clockwise/dextral or counter-clockwise/sinistral relative to the shear zone boundary) indicates the shear sense, while the amount of angular rotation of the marker from its original orientation allows calculation of the shear strain (γ) using the simple shear relation γ = cotθ' − cotθ, where θ is the marker's original angle to the shear zone boundary and θ' is its deflected angine within the zone.