Shown below is an example of how the subroutine 2000 can be altered to increase the
accuracy of the returned value. Here line 2020 obtains four successive readings
from the Light Pen. These are averaged in the next line, and then a check is made
that all four lie close to the average value. (If you leave out the check and C1-C4
vary widely you may find strange values like Col=129 appearing!). The routine might
be improved by including a small delay between the calls to USR0. Only two calls
with a reasonable delay between them may be enough....experiment!