GPS can be a very useful tool, but like all others tools it needs to be
implemented correctly.  Three of the biggest problems in using GPS that I
have encountered include not knowing the datum for the captured coordinates
(are then in UTM, State Plane, Decimal Degree, NAD27, NAD83, WGS72
HPGN/HARN, meters/feet ..etc); not applying the correction to the data
(before selective availability was turned off); and not tracking enough
satellites to give an accurate reading (mostly from hilly/heavy vegetation
areas).

The following link is to an article about the effect of turning off
selective availability on GPS.  Also see GPSWorld, June 2000 for another
article on the same subject.
http://www.geospatial-online.com/0600/0600divis.html

This article gives a good brief explanation on how selective availability
affected GPS.
http://www.geoplace.com/gw/2000/0008/0800gps.asp

And this article discusses the difference between accuracy and precision
with GPS.
http://www.geoplace.com/gw/2000/1000/1000gps.asp

Just some thoughts and suggestions for reading.

howard

Howard Beverly
GIS Analyst
Archaeologist
System Administrator
Wilbur Smith Associates
Lexington, Kentucky
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