The gradient of a straight line is a measure of how steep a straight line is.
The method to calculate the gradient is:
| Change in Y | |
| Gradient = |
|
| Change in X |
Because your line is drawn to pass through the origin of the graph, calculating the gradient is especially easy.
Simply pick any point on your line, then read off the position along the y-axis (radial velocity, in km/s) and the x-axis (distance in millions of light years) for that point and then divide them as above.
For example, if your point is at a distance of 1400 million light years, and a radial velocity of 32000 km/s, the gradient is
gradient = 32000 / 1400
= 22.9 km/s/Mly