Corrections for the Van Horn thesis

In reanalysing the Van Horn data for a recent paper, a couple of minor errors in the thesis became apparent.

1. Table 5.1, p.156. The labels for the distance between the holes seems to have become reversed, making it look as if the wider hole spacing was faster than the narrower hole spacing. Having checked with the original data it is clear that the opposite is the case. The labels in the first column should therefore read, from top to bottom, 3.75 cms, 2.00 cms, 2.25 cms, and 1.50 cms. None of the analyses are affected.

2. Fitts' Index of Difficulty. The calculations for Fitts' Index of Difficulty in chapter 5 of the thesis are not quite the same as those in a paper we have recently written. We are currently investigating the discrepancy.