What is the purpose of two grounding rods? And, what is the code for distance between the two?

Used for the code section about less than 25 ohms on ground rods or install 2 rod. the distance is not less than 6' apart Reference is 250.56 or .58 in 99 NEC, sorryI'm not under 2002 NEC yet.

The purpose is to insure a resistance of <25 ohms. Some of our local jurisdictions will allow only 1 if we want to set up the megger and prove to them that it's <25 ohms. Needless to say it's cheaper, quicker and easier to just install 2