Your Blogmeister’s Hotel Room
One of my prob/stat professors taught me, and everyone that ever took her course, I presume, that a very quick and dirty way to estimate the standard deviation of a data set is to subtract the bottom bookend from the top bookend and divide by six. Because virtually all data points (99.74%, according to the normal distribution) are within three standard deviations of the median.
I finally figured out this is why we still hang on to miles per hour and Fahrenheit. MPH works very well for ground level automobile travel, and F works well for mid-latitude temperate climate air temperature, because there are 100 gradations ranging from zero to one hundred between almost all of the real world practical possibilities. Almost all of the time, the temperature is between 0 and 100 F, any deviation on either side is considered newsworthy and noteworthy. As a bonus, Earth’s average temperature is 59 F, a little more than halfway up from the bottom end to the top end. Almost all of the time while traveling in an automobile, you’re going some number above 0 MPH but you very rarely top 100 MPH. To wit, the highest posted American speed limit is 85 MPH, close to the top bookend.
In the metric system, this neat centigradation does not present in either scenario.