How do you measure the gradient of a straight line joining two points?

There is a simple method for working out the gradient of a straight line joining any two points, for which the X and Y coordinates are known. For instance, if our first point is: A(X₁,Y₁), and our second point B(X₂, Y₂) then the gradient we are looking for is the gradient of the straight line AB, which joins the two points. This value is the difference in the Y coordinates, divided by the difference in the X coordinates, given by the equation: (Y₂ - Y₁) / (X₂ - X₁).

So, if the points are A(5, 2) and B(10, 4), then the gradient of the line AB would be: (4 - 2) / (10 - 5) = 2 / 5 = 0.4