Precision refers to how reproducible your measurements are. Typically, if you make multiple measurements of the same thing, your individual measurements will be a little off each time. It’s difficult to get the exact same measurement every time because there are so many sources of error. If your measurements are precise, then your measurements will be all pretty close to each other.

Accuracy refers to how close your measurements are to what you are really trying to measure.

So, imagine a bathroom scale that is miscalibrated. Every time you step on the scale, it reads 2000.142 pounds. So, that scale is precise (because it always gets the same measurement when you stand on it), but not accurate (because you don’t weigh anything near 2000.142 pounds).

Actually, it’s possible to be accurate without being really precise. Imagine that your real weight is 150 pounds, and every time you stand on it you get a measurement between 145 to 155 pounds. This scale is far more accurate than the first scale, even though it is not as precise. I guess they’re saying that if the scale was extremely inprecise (i.e. it measures anywhere from 100 to 200 pounds for a 150 pound person) then it isn’t terribly accurate.