Here is a couple of links, just the first two Google hits

http://www.extech.com/instrument/pro...ialMeters.html

http://www.stayonline.com/detail~ID~2048.html


"nothermark" wrote in message
news
On Sun, 4 Dec 2005 21:11:23 -0500, "Ivan Makarov"
wrote:

Apparently Joe is talking about contact resistance between a grounding
rod
and the soil. Is that correct, Joe? I also saw those ground rod clamp
testers in the Inet, and is still puzzled how they claim accuracy down to
0.01 Ohm.

Thks,
Ivan


Accuracy as in reading + or - 0.01 vs reading of 0.01 ohms absolute -
very big difference in technology involved. ;-) You have to define
what they are doing.