On Tue, 02 Sep 2008 12:47:07 -0700, BottleBob
wrote:


Accuracy:
Accuracy refers to the closeness between measurements (observations)
and their expectations ("true" values). The farther a measurement is
from its expected value, the less accurate it is.

Precision:
Precision pertains to the closeness to one another of a set of
repeated observations of a random variable. Thus, if such observations
are closely clustered together, then these observations are considered
to have been obtained with high precision.


An easier visualization:

Accuracy - all in the 10 ring

Precision - a 0.375" group, but it might be anywhere on the target.


RWL