A ~unit strain~ is the strain per unit of length.

Thus if a post 10 inches long before compression is 9.9 inches long under the compressive stress, the total strain is 0.1 inch, and the unit l 0.1 strain is -- - = -- --- = 0.01 inch per inch of length.
L 10 As the stress increases there is a corresponding increase in the strain.

This ratio may be graphically shown by means of a diagram or curve plotted with the increments of load or stress as ordinates and the increments of strain as abscissae.

This is known as the ~stress-strain diagram~.

Within the limit mentioned above the diagram is a straight line.