Signal reacquisition, nominally expected at approximately 2:26 a.m. PDT did not occur. Efforts to find and communicate with MCO continued up until 3 p.m. PDT on September 24, 1999, when they were abandoned.’3

The spacecraft was 60 miles (96.6 km) closer to the Martian surface than the mission controllers thought, and $125 million disappeared into the red Martian dust. The loss was bad enough but when the cause was discovered it looked like a case for the force-feeding of humble pie. Lockheed-Martin, the company controlling the day-to-day operation of the spacecraft, was sending out data about the thrusters in Imperial units, miles, feet and pounds-force, to mission control, while NASA's navigation team was assuming like the rest of the international scientific world that they were receiving their instructions in metric units. The difference between miles and kilometres was enough to send the craft 60 miles off course on a suicidal orbit into the Martian surface.4

The lesson of this débâcle is clear. Units matter. Our predecessors have bequeathed us countless everyday units of measurement that we tend to use in different situations for the sake of convenience. We buy eggs in dozens, bid at auctions in guineas, measure horse races in furlongs, ocean depths in fathoms, apples in bushels, coal in hundredweight, lifetimes in years and weigh gemstones in carats. Accounts of all the standards of measurement in past and present existence run to hundreds of pages. All this was entirely satisfactory while commerce was local and simple. But as communities started to trade internationally in ancient times they started to encounter other ways of counting. Quantity was measured differently from country to country and conversion factors were needed, just as we change currency when travelling internationally today. Once international collaboration began on technical projects the stakes were raised.5 Precision engineering requires accurate inter-comparison of standards. It is all very well telling your collaborators on the other side of the world that they need to make an aircraft component that is precisely one metre long, but how do you know that their metre is the same as your metre?

MEASURE FOR MEASURE – PAROCHIAL STANDARDS

‘She does not understand the concept of Roman numerals. She thought we just fought World War Eleven.’

Joan Rivers6

Originally, standards of measurement were entirely parochial and anthropometric. Lengths were derived from the length of the king's arm or the span of his hand. Distances mirrored the extent of a day's journey. Time followed the astronomical variations of the Earth and Moon. Weights were convenient quantities that could be carried in the hand or on the back. Many of these measures were wisely chosen and are still with us today in spite of the official ubiquity of the decimal system. None is sacrosanct. Each is designed for convenience in particular circumstances. Many measures of distance were derived anthropomorphically from the dimensions of human anatomy. The ‘foot' is the most obvious unit of this sort. Others are no longer so familiar. The ‘yard’ was the length of a tape drawn from the tip of a man's nose to the farthest fingertip of his arm when stretched horizontally to one side. The ‘cubit’ was the distance from a man's elbow joint to furthermost fingertip of his outstretched hand, and varies between about 17 and 25 of our inches (0.44–0.64 metres) in the different ancient cultures that employed it.7 The nautical unit of length, the fathom, was the largest distance-unit defined from the human anatomy, and was defined as the maximum distance between the fingertips of a man with both hands outstretched horizontally to the side.

The movement of merchants and traders around the Mediterranean region in ancient times would have highlighted the different measures of the same anatomical distance. This would have made it difficult to maintain any single set of units.