After manually correcting the main tracking errors (see Correct Tracking Errors in the Table of Contents), you can refine the centers of the marker positions using a polynomial fit. This should be done for round markers, but not for conical markers.

It is best to save your dataset first. Refining by polynomial fit cannot be undone, and while it usually makes the data better, it doesn't always help. Save your file, and then save a second version and add polyfit to the filename, so that you can compare the versions afterward.

Select all of the points that you want to refine, right-click, and select "Refine centers of selected Points by polynomial fit." The default is to refine points that were automatically tracked or set from the main window, but not those that were set from the detailed view. You can choose to change this and only refine those that were tracked, or refine all. Specify the range of frames.

If you are refining a single point, it is helpful to have its reprojection error open in the plot window while you refine so that you can see the effect of the polynomial fitting in real time.

The refinement may cause the reprojection error to increase for a few frames, and this can be corrected manually for each point. Save the dataset and then reopen the original file (before fitting) and compare the reprojection errors to make sure that the fitting did not make the errors worse.

Aim for mean reprojection errors that are less than 0.2 pixels for all points. The mean is shown at bottom of the plot window.