1068: Differentiation - Ln x - Gradients of ln ax

The graph of $\color{blue}{ f(x) = \ln (a \, x) }$ is shown in blue, together with its tangent and gradient at a sample point in red.

By considering the gradient at x = 1, 2, 3, 4, can you predict what the gradient function of $\color{blue}{ f(x) = \ln (a \, x) }$ is?