Shear strain is an angular measure associated with the change in shape of the object. To determine the shear strain at corner $\mathrm{P}$ of the plate, the angle at corner $\mathrm{P}$ must be determined both before and after the $1 \mathrm{mm}$ vertical deflection of corner $\mathrm{P}$. The shear strain $\mathrm{\gamma }$ is the difference between these two angles, measured in radians.