http://www.factmonster.com/ipka/A0001660.html

http://www.co.lake.mn.us/index.asp?Type=B_BASIC&SEC=%7BF40A381C-9A4A-49EC-8175-5126B0324963%7D

http://www.co.otter-tail.mn.us/gis/landmeasurements.php

What is Acre?   http://www.wisegeek.com/what-is-an-acre.htm

Land Measurements in India   http://www.indiahousing.com/land-terminology/land-measurements.html

http://landportal.gsfc.nasa.gov/  NASA

http://en.wikipedia.org/wiki/Imperial_units

http://www.americanheritage.com/articles/magazine/ah/2002/6/2002_6_44.shtml

http://www.reference.com/motif/Reference/acres-land-measurement

http://www.unc.edu/~rowlett/units/custom.html

http://www.sensorland.com/

http://www.britannica.com/EBchecked/topic/4100/acre

http://www.biometrics.mtu.edu/fw2050/lectures/Lecture%209%20-%20Land%20Measurements%20and%20Map%20Use.pdf

http://www.hgsubsidence.org/about/subsidence/measure.html