The original avoirdupois pound
Some historical background
In my last article, I mentioned the avoirdupois pound, but I avoided any side story about this measurement unit to focus on the horsepower story. But after researching its origins and evolution, I discovered, IMHO, a fascinating story.
The avoirdupois system is a system for the measurement of weight developed in the XIII century. It employs pounds and ounces as basic measurement units. The most accepted relationship between a pound and an ounce was that 1 pound contained 16 ounces. Why sixteen ounces?
A long time ago…
Because, for Middle Age Europeans, calculations were easier using the number 16, which has three even numbers as divisors: 2, 4, and 8. So, it was easy to measure a pound, half a pound, half of half a pound, and the almost inconceivably complex half of a half of a half pound, in ounces.
On behalf of Middle Age Europeans, we must consider that these people had a few other things to worry about other than weight measurement systems, like the black death, their feudal lord’s greediness, and most of all his lust. So, the avoirdupois system persisted through the ages. Avoirdupois means “goods of weight” in Anglo-Norman French, which was the language employed by England’s nobility in those years. But let us focus on physics and leave linguistics for another day.
The avoirdupois system was declared as England’s official weight measurement standard by King Henry VIII and remained unchanged until 1588. The feudal tradition of lust had persisted and was dutifully kept by Henry by having six wives, one after another.
Into the age of empires
Henry VIII’s daughter, Queen Elizabeth I, modified the avoirdupois pound to include smaller units and defined the pound as being equal to 7000 grains. A grain is the ideal weight of a single grain of cereal, although it is not mentioned anywhere what kind of cereal was used as a reference.
By the way, again, 24 grains equal one pennyweight, 20 pennyweights equal one troy ounce and 12 troy ounces equal one troy pound. Old measurement systems seem to be favored by old business activities like the precious metal market, which still employs the troy ounce as a weight measurement unit for gold.
When the British Empire ruled the world…
After Queen Elizabeth, the avoirdupois system was changed again and included in the British Imperial System (BIS) of measurements, including new units for larger weights. In the BIS, 14 avoirdupois pounds equal one stone, 2 stones equal a quarter or 28 pounds, 4 quarters equal 1 hundredweight or 112 pounds and 20 hundredweights equal a long ton or 2240 pounds.
A smaller unit was added to the system, until then, the smallest weight employed was the “part” or 1/16 of an ounce or 1/256 of a pound.
The final iteration of the avoirdupois system was the one that still today is part of the BIS:
| Unit | Relative value | Metric value | Notes |
| drachm or dram (dr) | 1/256 | ≈ 1,772 g | 1/16 oz |
| ounce (oz) | 1/16 | ≈ 28,35 g | 16 dr |
| pound (lb) | 1 | ≈ 453,6 g | 16 oz |
| stone (st) | 14 | ≈ 6,350 kg | ½ qr |
| quarter (qr) | 28 | ≈ 12,70 kg | 2 st |
| long hundredweight (cwt) | 112 | ≈ 50,80 kg | 4 qr |
| ton or long ton | 2240 | ≈ 1016 kg | 20 cwt |
If you are a metric individual, like me, you are surely feeling strong emotions right now. I just felt pity towards British engineers, who had to work with this unbelievable concoction of a system.
Finally, common sense arrives at the UK
In the Weight and Measures Act 1985, the British law redefined the Imperial System in terms of the metric system equivalent units and declared its use illegal for trade activities, except for milk, beer, and cider which can be sold by the pint. A pint is a volume of 568.26125 milliliters, or the volume occupied by 20 Imperial ounces of distilled water.
Nowadays, in the UK the metric system is used in business and technology, but the Imperial System still lingers in daily life.
In 1995, the transition to the metric system was complete, but certain uses persist in the public, like in distances (miles, yards, feet, and inches). A survey made in 2015 showed that in the UK, people over 40 preferred the BIS, but those under 40 preferred the metric system.
It seems that, in the UK, the BIS will last a couple of generations more before falling into oblivion.
Meanwhile, in the land of the freedom, home of the brave…
Let us go across the pond to visit the USA and before landing we better look at the US Customary units’ system.
The USA adopted the 1824 version of the BIS but did not adopt any of its later modifications. The US version of the avoirdupois system has some curious features, like the use of the grain and the dram as base units for the measurement of gunpowder charges, especially for shotguns and large rifles. The US obsession with firearms permeates deeply through the country’s culture.
The US customary system employs the following version of the BIS:
| Unit | Relative value | Metric value | Notes |
| grain (gr) | 1/7000 | ≈ 64,80 mg | 1/7000 lb |
| dram (dr) | 1/256 | ≈ 1,772 g | 1/16 oz |
| ounce (oz) | 1/16 | ≈ 28,35 g | 16 dr |
| pound (lb) | 1 | ≈ 453,6 g | 16 oz |
| quarter (qr) | 25 | ≈ 11,34 kg | 25 lb |
| short hundredweight (cwt) | 100 | ≈ 45,36 kg | 4 qr |
| ton or short ton | 2000 | ≈ 907,2 kg | 20 cwt |
The strange emotions metric people feel when they discover the bonkers relationships used in the BIS surely now have turned into a creeping chill going through their spine: the measurement system employed by the USA is the same that was used in England when Queen Elizabeth I was the country’s ruler.
An urban myth
Some people from the US like to justify this anachronism, saying that their country was able to get to the moon using nonmetric measurements. But this is simply not true, is a lame urban myth. This was probed with the release of the source code of the navigation programs written by NASA in the sixties.
The truth is that the Apollo Moon Landing project employed SI units in all the critical parts of the missions. The famous navigation computers used in the LEM landing module and the Apollo Command module used metric measurement units. The nonmetric myth was born because the computer’s display showed distances in feet and nautical miles, but the internal calculations were performed using metric units.
By using the metric system, NASA engineers were able to program and perform the required calculations in the Apollo computers because they discarded the use of nonmetric units. Otherwise, the computers would have run out of memory due to the extra multiplications required to use US customary units.
Last thoughts
In a world that has adopted the SI measurement system, it is symbolic that just three countries on the whole planet refuse stubbornly to abandon the use of the BIS.
Which are those three countries stuck in the Elizabethan era? They are Liberia, Myanmar, and the USA. Go figure…