Man has always had a need to measure distance, and these distances have been based on human beings and what we can accomplish. This is why measurements like 'axe-cast', 'spear-cast' and 'arrow-shot' felt quite natural and obvious to earlier generations. The distances were not that precise, but people got the idea anyway.

Work on Empire State Building, 1930s.With the Romans came a demand for more precision. They introduced the concept of milia, from mille passus, which later became 'mile'. Mille passus quite simply means 'a thousand paces'. A pace was five feet, so a milia would be equivalent to 1,478 metres today.

During the time of the French Revolution, the order of the day was 'out with the old, in with the new' to try and make life easier. In 1790, Talleyrand's national assembly ordered the Royal Academy of Sciences to produce a system of measurement units 'For all times, for all people'. The Academy presented a brand new system of length – the metric system.

Almost 100 years later the metric system was officially introduced in Sweden, following a proposal by K O Wallenberg. The old distance measurements were to be gradually phased out over a transitional period of 10 years. In 1889 it became illegal to use old Swedish inches in trade and commerce.

But how could ordinary folk use these new-fangled metres and centi-metres when they had learnt to measure in inches? This was a problem that certainly needed solving!

Imagecaption=Karl-Hilmer Johansson Kollén.And the solution was not that far off. In Stockholm at that time, there lived a headstrong architect called Karl-Hilmer Johansson Kollén. He was commissioned to design details for a theatre, but refused on religious grounds and resigned his position. Who would dare do that these days…? And how was he to earn a living now?

Karl-Hilmer realised the educational value of being able to see both measurement systems at the same time, so he developed a comparison rule.This was quite simply a measuring rule that showed both the old inches and the new centimetres. The problem was that the rule was awkward to handle in a single long piece. Enter Karl-Hilmer's next innovation – the folding rule.Imagecaption=Karl-Hilmer Kollén's comparison rule.

The capital of SEK 5,000 came from an English lady who had heard about the new ideas and wanted to invest in them. Thus the rule manufacturing company Svenska Mått- och Tum-stocksfabriken saw the light of day, and generated many times the return on the original investment. Today the company is Hultafors AB – still the leading manufacturer of folding rules in Sweden.

Imagecaption=Old commercial plate.Since the beginning, sales of folding rules have developed dramatically, and their total length would easily stretch several times round the globe.

The folding rules come in different materials – aluminium, fibreglass or standard wood – depending on the environment they are to be used in. The wood used is no longer the original 'genuine folding rule wood' as mentioned in old advertisements. Until the 1960s the rules were made of Swedish whitebeam (similar to rowan), but since then downy birch has become the new original.

There are still different lengths of inch. Hultafors folding rules no longer show old Swedish inches, but rather British imperial inches. At 25.4 mm, the imperial inch is slightly longer than the Swedish inch's 24.7 mm.

Imagecaption=Downy birch in Sweden.

However, there are also Norwegian and Danish inches (26.15 mm) which have increased relative to the imperial inch. The reason for this – as rumour has it – is that everything used to be measured in imperial inches. However, when timber cargoes reached Britain on ships from Denmark, the measurements never matched up, as the timber had dried slightly during transport. To solve the problem, the Danes officially increased the length of their inch to compensate for the drying-out on the voyage to British shores!

Hultafors folding rules marksSo what can you measure with a folding rule today? Well obviously they give a high-precision reading in either just the metric system, or the metric and imperial systems.

At the beginning of the rule there are a few small figures in brackets, along with a III in Roman numerals. This is an official EU marking to indicate that the measuring tool is precise enough to fulfil certain pre-specified measurement directives.

At 8.5 cm along the rule is a triangular red symbol comprising the letters KHJK. This is none of your international mumbo-jumbo, but simply Hultafors' own corporate symbol.

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