50 feet = 15.24 meters.

So that's the number we should use, right?

Wrong! At least in most cases, when we write "50 feet", we don't mean 50.00 feet.

We may mean 50

__+__1 feet, 50

__+__5 feet, 50

__+__10 feet, or even 50

__+__25 feet. Each "translates" differently.

50 feet converts to 15.24 meters, 51 feet to 15.5448 meters (using http://www.onlineconversion.com/length_common.htm), and 49 feet to 14.9352 meters; so 50

__+__1 feet should be converted to 15.2

__+__0.3 meters. (The extra two or three digits do not provide more accuracy here).

Similarly, 55 feet converts to 16.764 meters, and 45 feet to 13.716 meters; so 50

__+__5 feet should be converted to 15

__+__2 meters. 60 feet converts to 18.288 meters, and 40 feet to 12.192 meters; so 50

__+__10 feet should be converted to 15

__+__3 meters. Notice that the "translated" uncertainty for 10 feet is not the double of what it was for 5 feet!

Finally, the error for 50

__+__25 feet is calculated as follows: 50 feet converts to 15.24 meters; 75 feet to 22.86 meters, and 25 feet to 7.62 meters; leading to a conversion of 50

__+__25 feet to 15

__+__8 meters.

If errors are not assigned, you are better off "translating" 50 feet as "about 15 meters."

A professor of mine used to say that a number is not complete without its uncertainty assessment. Another unrecollected source distinguished between "naked numbers" -- without uncertainty values -- and "clothed numbers" -- those with uncertainty listed. Try not to let your numbers freeze this winter.