Good description and diagram of Accuracy vs Precision?

You can shoot some number of arrows (call the number N) at a target. If all N are in the bullseye, then you're both accurate and precise. If they're within a small circle high and left of the bullseye, you're precise but not accurate. If you're within a large circle centered on the bullseye, you're accurate but not precise.

The accuracy or the error in a measurement is the actual value of a parameter minus the measured value. Precision relates to how repeatable is the measurement. A measurement can be accurate and precise, one and not the other and neither. Take you example of measuring a car - lets say the car's actual length is 6.235 m or 6235 mm. If we measure the car to the nearest m and we do it five times. Since this is a fairly gross measurement we would probably get the same value each of the five times. Thus the measurement is very repeatable and therefore precise. However, its accuracy is about 1/4 m. If we measure the car to the nearest mm and we do it five times, we will probable get five different values. All ranging near the actual value. This time the measurements are far more accurate (with an error probably less than 25 mm vs 235 mm for the other) but its precision is less since we will have a spread of values.