mistake in 'Off Parallel'

My book 'Off Parallel' is dedicated to the land surveyors of America; members of a very inportant, but surprisingly underappreciated, profession. I'm curious to know if anyone, especially surveyors, who downloaded a copy of 'Off Parallel' before it was re-listed in late September of 2011, noticed a surveying-related error in the text. The mistake is pretty subtle so a hint is probably in order: the book's title and the latitude of Silver City, New Mexico should lead one to it.

Also, Thanks, Gary Proctor, for writing a review.