crushing load—the maximum compressive force applied to the specimen, under the conditions of testing, that produces a designated degree of failure.
modulus of elasticity—the ratio of stress (nominal) to corresponding strain below the proportional limit of a material. It is expressed in force per unit area based on the average initial cross-sectional area.
offset compressive yield strength—the stress at which the stress-strain curve departs from linearity by a specified percent of deformation (offset).
proportional limit—the greatest stress that a material is capable of sustaining without any deviation from proportionality of stress to strain (Hooke's law). It is expressed in force per unit area.

Typical stress-strain curve
The behaviour of a material in compression often differs from that of the same material in tension. For ductile metals, as shown below, it is often observed that failure will not occur in compression —a striking example is cast iron, which is extremely brittle in tension but is very malleable in compression.
Notice that in compression, the axial stress and strain are negative and therefore the stress–strain curve is correctly plotted in the third quadrant. (This convention is not followed in much of the civil engineering literature where, by convention, compressive stresses are regarded as positive.) For most materials that yield, the yield stress in compression is approximately equal to the yield stress in tension.
Since the axial strain is now negative, the magnitude of the "true strain" will be larger than that of the nominal strain. Also, since the current area A is larger than the original area A0 , the magnitude of the "true stress" will be smaller than that of the nominal stress. The combined effect of these relations is that points on the "true stress– strain" curve will be algebraically above and to the left of corresponding points on the nominal stress– strain curve, just as they were in tension. Remember again that the formulas for "true stress" and "true strain" written in terms of the nominal strain are valid only when the deformation is homogeneous, that is, they are valid only if the original cylindrical shape of the specimen is retained during testing.