About Strain Measurement
What is Strain?
Change per unit length in linear dimension, usually expressed as a percentage.
Load on a specimen divided by the cross-sectional area through which it acts.
The complete stress-strain curve is important because it allows you to know not only the maximum stress and strain a material can handle, but also important properties such as stiffness and yield (where the material becomes completely deformed), and ultimately, how the material will behave in use.
Why is Strain Important?
...Although it does not appear to have failed, the rubber band no longer has the same dimensions or mechanical properties, which will alter the way it performs in use.
If this were your product, you can see how this would be considered a failure!
Most international material testing standards recommend or require that you measure strain.
Have you considered the consequences of not measuring strain properly?