It is easy to explain these by treating the specification as a target for a gun. Shots that hit the target are good, while those that miss are out of specification. We have a good idea of what accuracy is. If we are shooting at a target, we want to be aiming at its center. However, even if we are aiming at the center, there is some unavoidable random variation in where the shots hit.
Precision is the opposite of variation.
A precise process has very little variation. A musket is a smoothbore gun that was common in the 15th through 18th centuries. Soldiers used them in the American Revolution and Napoleonic Wars. It is hard to hit anything with a musket at more than 100 to 150 yards, no matter how good the shooter is. Figure 3-1 shows a simulation of 100 musket shots at a target.