As fledgling conservation students, we are encouraged to get a good grounding in the techniques, tools and materials that were used to make the original objects that we now conserve. For example, we use hide glue for making glued joints, wooden moulding planes for making specific profiles and hand tools such as chisels, planes and saws for shaping wood or metal.

We are also meant to pick up some historical context for the items that we deal with. We learn about historical makers, trends in design, and how notable objects have been conserved and repaired. However, there is one important piece of historical context that is not often emphasised - and this is the measurement system.

Most people know that the metric system was introduced in France, associated with the whirlwind of new legislation and standards that followed the French Revolution. However, it is less obvious why this occurred, and why it occurred in France rather than in England or elsewhere.

In England, the system of measurement had been unitary more or less since the Magna Carta, which had decreed that 'There shall be one unit of measure throughout the realm'. A significant amount of effort by local government went into policing this, mainly to ensure that people were not sold short weight or volume.

In France, on the other hand, the system of measurement handed down from Charlemagne had fractured into many hundreds of competing units by the eighteenth century, which meant that different regions of France would mean very different things by what should be standard measures of weight, distance or volume. Clearly then, there was a pressing need for the metric system in France, much less of a need in England. For this reason, metrication came late to Britain and it can safely be assumed that many of the items we will be called upon to conserve would originally have been made in feet and inches.

One notable thing about using imperial measures is the tendency to select simple ordinal points (inches, half inches, quarter inches) when designing anything. As a case in point, a recent project to copy a nest of tables derived a set of measurements for the table leg, giving a set of measurements in millimetres that were precise but with no obvious relationship between them. On checking the measurements in inches, however, it became evident that all of them were done to the nearest quarter-inch (e.g 4", 41/4", etc) and that all the beadings were quarter inch in size.

Knowing this serves two purposes. Firstly, it gives insight into the design process, which will often select a measurement to the nearest inch or half inch rather than an arbitrary number of millimetres. Secondly, it allows us to recover information.

Rather like making a photocopy, any copying process (mechanical or otherwise) can lead to degradation of the original form and loss of information. If it is known, however, what the original measurements were meant to be, then an accurate version of the original can be made, with no errors - this will be a re-creation rather than a copy.

This is not an argument for going back to the imperial system. Anyone who has spent time in the engineering industry will recognise what a retrograde step this would be. However, there is an argument for being aware of it, understanding its place in design history, and being familiar with the units that form an integral part of the design of so many pieces.

As a first step, the aspiring imperial student should learn to recognise some common measurements and their metric equivalents.

If it looks like... Then it's probably ..
300 mm One foot (12 inches) (304.8 mm)
150 mm Six inches (152.4 mm)
75 mm Three inches (76.2 mm)
25 mm One inch (25.4 mm)
19 mm ¾ inch (19.05 mm)
12 / 13 mm ½ inch (12.7 mm)
6 mm ¼ inch (6.3mm)


Acres, poles, rods, perches, chains, furlongs, bushels, hogsheads and firkins will be left to a future essay!