Excessive precision is a way of concealing how good the numbers are.  For example, a 2011 ad for the Volkswagon Passat says it can go 795 miles on a tank of gas. This implies that 800 would be impossible, and that 790 is guaranteed, i.e., an accuracy of 5 miles. Actually, because of driving conditions or one's chosen speed there would be more variation.
- "A general rule is to give precisions approximately one tenth the size of the object, unless there is a clear reason for additional precision. Overly precise coordinates can be misleading by implying that the geographic area is smaller than it truly is."