Although most countries now use the Metric system or the United Kingdom Inch, it should be appreciated that, until comparatively recently, there were many completely different arrangements in use. In the 19th century James Chesterman & Co. of Sheffield, UK., ( a major manufacturer of rules and measuring tapes [note the word 'rule', this is a piece of measuring equipment which should not be confused with 'ruler' which is a person who governs a country!] ) maintained nearly 100 different standards of length and supplied rules and other measuring equipment marked in the local units of many countries.

It is interesting to realise that the great majority of countries did, like the UK., use a three unit system. The smallest unit approximated to an 'Inch' (meaning a 'twelfth part'), the intermediate unit was either ten or twelve times greater, approximating to the 'Foot', but the third unit could vary, being either three or six times greater than the intermediate unit.

This strongly suggests that all the systems had been independently developed in remotest times from units of the human body. It is generally assumed that the 'Inch' was the length of the first joint of the thumb, the 'Foot' being obviously derived as indicated by its name. The largest unit in the UK, the 'Yard' (from the Old English Gierde meaning rod), is supposedly the distance from the nose to the fingertip of a particular monarch and bore a relationship to the length of a longbow arrow. Those countries where the largest unit was approximately twice this had presumably used either a man's height or the total span of his outstretched arms. The 'Hand', as used in measuring horses, is the width of the palm of the hand, the 'Cubit' was the distance from the elbow to the fingertips, Noah supposedly using such a rule or tape, whilst the 'Barleycorn' was one-third of an Inch.

Despite the vicissitudes of fires and problems of standardisation it is interesting to note that the current Imperial Standard Yard (the basis in the UK) differs from remaining Elizabethan and earlier relics by only the odd hundredth of an inch.

Until the Revolution, the French used an interesting duo-decimal system. The Foot (Pied-de-Roi) was divided into 12 Inches. Each Inch broke down into 12 Lignes and each Ligne to 12 Douziemes. To a limited extent this system survived, particularly in Switzerland, to quite recent years. It was applied as a way of measuring and describing the dimensions of the mechanisms (movements) and components in the watch industry. A comparison is shown below:
             
  Paris Foot = 12.7908 English Inches = 324.89 mm
  Paris Inch = 1.0659 English Inches = 27.07 mm
  Ligne = 0.0888 English Inches = 2.26 mm
  Douzieme = 0.0074 English Inches = 0.19 mm

 

  All these systems had the great merit of being "user-friendly". in a fit of revolutionary fervour, the French decided that they would base a new standard (the Metre) on the distance between the North Pole and the Equator.

However, they could not reproduce this consistently and so, after several variations, resorted to the old standby, the length of a 'standard' bar of Platinum / Iridium alloy. Unfortunately, they confused arithmetical simplicity with 'user-friendliness'. Using a step of 10 was arithmetically simple but the actual decimal steps are not much use in the real world.

In actual practice the metric systems used are nowadays based on a unit step of 1000 rather than a step of ten. Consider that we usually use the following selections from the decimal range:
       
  micrometre = metre x 10-6
  Millimetre = metre x 10-3
  Metre    
  Kilometre = metre x 103
   
  For all practical purposes the intermediate units of centimetre, decimetre, decametre and hectometre are obsolete.
   
  The writer of this article, Jim Nicholson, worked for James Chesterman & Co.

as a production engineer for a number of years until the company closed.