Since the new year will soon be upon us, this number is a good one for the engineer. It is the estimation (because it is difficult to measure absolutely precisely), the number of days in a year. Sure, we can be more precise, but for calendar calculations, down to the 10,000th of a day is precise enough for roughing out engineering calculations that will involve longer time frames, such as the cost per year of operating a waste-water treatment facility.

Note that the fraction is why we have leap year every four years. It is almost 1/4 of a day, so adding the day every four years keeps us close to the same start and end of the year, rather than having the seasons shift months if we didn’t have leap years. Of course, we haven’t even begun to discuss the slowing of the earth’s rotation over time. Maybe we will save that for a later post.

Engineers like precision. Instead of a year being 365 days, or even 365 1/4 days, think about a more precise 365.2422 days.