These units can also be seen as units of force per unit of area (negative pressure), and the "ij" element of the tensor can also be interpreted as the force parallel to the "i"th axis suffered by a surface normal to the jth axis per unit of area. Indeed, the diagonal elements give the tension (pulling) acting on a differential area element normal to the corresponding axis. Unlike forces due to the pressure of an ideal gas, an area element in the electromagnetic field also feels a force in a direction that is not normal to the element. This shear is given by the off-diagonal elements of the stress tensor.