Final answer:
Contrast on a characteristic curve is measured by finding the tangent at a specific point, which is equal to the slope at that point.
Step-by-step explanation:
Contrast can be measured from the characteristic curve by finding the tangent of the curve. The slope of a curve at a specific point is equal to the slope of the tangent line at that point. This principle can be used to determine various properties such as instantaneous velocity in a position versus time graph, or to calculate instantaneous rates of change in other contexts.
To find the slope of the tangent, one must identify two points on the tangent line, and use these to calculate the rate of change.
To illustrate, if given a point Q at t = 25 s on a curve, and the endpoints of the tangent correspond to a position of 1,300 m at time 19 s and a position of 3,120 m at time 32 s, one can plug these endpoints into the slope formula to find the instantaneous velocity at t = 25 s.