How do you measure the rods? Presumably the direct measurement method using another substantial piece of buried metal?
What is the limit of resistance permitted for your grounds in an installation?
For a circuit breaker or fuse to work properly on a fault then the ground must be of low enough resistance.
The higher the resistance of the ground the slower the circuit breaker will react to the fault.
We have rules on how fast we need a circuit breaker to operate, in the UK this is 0.4seconds for final circuits and 5seconds for distribution circuits (there's more to it than this but I'm keeping it simple here)
So we can calculate the maximum ground resistance permitted to achieve the required disconnection time.
From this we can calculate the size of ground needed and also test it after installation to ensure compliance.
You say we are talking about no resistance at all, but that's not true, every conductor has resistance. The resistances are very small, but so are the limits for correct operation of a circuit breaker.
The limits can be well below 1 ohm and so accurate calibrated testers are needed