A small motor was used to rotated the upper glass slide at a constant rate of 0.5 revolutions per hour, which produced a relatively smooth, non-coaxial circular (Figure 5). Couette flow in the paraffin in the annular shear zone. Flow lines are circular but parallel to the frosted grips and the flow pattern therefore bears a resemblance to that of simple shear: no stretching occurs parallel to the grips. A circle parallel to grips is defined as flow circle, similar to the flow plane of simple shear (Ten Brink & Passchier 1995). The experiment was conducted at a homologuous temperature (T/T_melting) of 0.88. The circular shape of the specimen chamber induces a gradient of increasing flow stress and strain rate over the sample. A gradient in shear strain rate exists, decreasing in paraffin from inner shear zone boundary to the outer in relation to , where r is the distance from a position in the annular shear zone the rotation axis (Figure 6) (Masuda 1994). The imposed annular shear strain (g) is calculated as a circular displacement of the outer frosted grip, divided by shear zone width (Passchier & Sokoutis 1993).