title: After fitting a linear function to a set of data, how can I find the error on the gradient of the function?
body: <p>I currently fit a linear function to distance vs. time graph in order to work out the velocity of a particle...</p>
  
  <pre><code>velocity, intercept = numpy.polyfit(time, displacement, 1)
  </code></pre>
  
  <p>How can I then find an estimate of the error in this velocity measurement?</p>