Inches, ounces, gallons …. Why??

Although, apparently, the USA and Myanmar are the only nations which still fully use Imperial units in everyday life, there are many others around the world which use some imperial measurements. I live in the UK, and was brought up not only using imperial units for measurement, but also for currency: 12 pence to 1 shilling, 20 shillings to 1 pound. Much time and effort was taken up in primary education learning (in those pre-calculator days) how to do money calculations. “How much change do you get from a £10 note when you buy 3 items each costing 1 pound, 8 shillings and 11 pence?” – written, incidentally, as £1 8s 11d or £1 8/11d, the “d” going back to the Roman denarius. (Answer below). The decimal system has huge advantages, of course: prefixes such as kilo, centi and milli apply to all units of measurement; and decimal calculations are generally easier than non-decimal.

Mathematically, though, I don’t view 100 as a particularly “nice” number because it has so few factors: 2, 5, 10, 20, 25 and 50, other than 1 and 100. It follows that a pound, or a dollar, or a metre, cannot be divided up into many smaller parts. Now, with 12 pence to a shilling and 20 shillings to a pound, a pound contained 240 pence – and 240 is lovely! An imperial pound could be divided by 2, 3, 4, 5, 6, 8 ….and so on, making 18 factors other than 1 and 240. So a third of a pound was 80 pence, or 6/8d. And the nice numbers go on:

Length:    12 inches to a foot, 3 feet to a yard, giving 36 inches to a yard.
1760 yards to a mile, with factors 2, 4, 5, 8, 10, 12 ….. (22 of them!)

Weight:     16 ounces to a pound (lb), 14 lbs to stone, 8 stone in a hundredweight (cwt), 20 cwt in a ton, giving 2240 lbs to a ton – coincidentally about the same weight as a metric tonne.

The Imperial system is easy to use if you’re brought up with it. I think this is because it developed through everyday use, unlike the metric system which was artificially based on naturally occurring units – a metre, for example, was originally defined as one ten-millionth of the Earth’s circumference. In particular, you never have to deal with very big numbers: the desk I am working on is 2 feet 6 inches wide, which is easier for the senses to grasp than the metric equivalent of 76cm.

And, of course, there is one universal unit which we don’t measure in 10s or 100s, and that is time. 60 seconds = 1 minute, 60 mins = 1 hour, 24 hours = 1 day. This means that it is easy to divide an hour up into 3 equal parts (20 minutes each), or a day into 8 equal parts (3 hours each), which would be much harder if there were, say, 100 minutes in an hour and 100 hours in a day.

 

Answer to money calculation:  £5 13/3d

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