One nice thing about a GPS is you can get an accurate speed reading to
check your speedometer against.  My Vanagon speedometer turns out to be
very accurate -- it's only off 1 mph at 60.  Much better than my Honda,
which is already off 5 mph at that point, and worse the faster I go.

David Brodbeck, N8SRE
'82 Vanagon Westfalia Diesel
'94 Honda Civic Si