On Mon, 20 Jan 2003, Aristotle Sagan wrote:

> Drive 10mph faster than what you think you should.

Or, if you find the error isn't consistant, you could make up a correction
chart.  That's what I did on my Honda -- made up a little piece of paper
with two columns, actual speed on one side and indicated speed on the
other, and taped it to the dash.  A short drive with a GPS and a tape
recorder (or a passenger to take notes) should provide all the data you
need.  I focused on the speeds that are common as speed limits in my area.

             _ _
  __ _ _   _| | |  | David M. Brodbeck (N8SRE)              Ypsilanti, MI
 / _` | | | | | |  +-----------------------------------------------------
| (_| | |_| | | | @ cyberspace.org
 \__, |\__,_|_|_| "To the optimist, the glass is half full.  To the
 |___/             pessimist, the glass is half empty.  To the engineer,
                   the glass is twice as big as it needs to be."