2 inches is a very useful measure for a lot of things. I know that the middle digit on my little finger is an inch, and my foot is actually a foot long. I have

2 inches is a very useful measure for a lot of things. I know that the middle digit on my little finger is an inch, and my foot is actually a foot long. I have no idea what 5mm looks like unless I convert it. Also, don't forget that wonderful measure of area, the acre. I have no idea how big a hectare is, only that it's less than an acre. And there are 640 acres to a square mile, which is convenient if you grew up in farm country where there is a road pretty much every mile. I won't bore you with gallons, chains, rods, furlongs, or hundredweights (American or Imperial).