One foot per nano-second

If anyone ever asks you how fast light travels, you might like to tell them

One foot per nano-second!

Translating that into metric units it is about 30cm in a billionth of a second (where this is a UK billionth - namely one thousand millionth of a second).

Not many people know that!  But for some of us it is actually a useful rule-of-thumb in our daily work.

You might also like to surprise someone with the unit of a micro-century.  Just between you and me, that is just over an hour.  Business meetings should generally limited to a micro-century.  In that time, light manages to travel about 750 million miles.