Metrication

Metrication is an add-on for Firefox that identifies Imperial/US customary units and converts them to appropriate metric units.

When an Imperial/US unit is identified, Metrication hides it and inserts an appropriate metric value and unit so that the document reads as if it were originally written for a metric audience.

The replacement metric value and unit are embedded within a hotspot that will popup a small window containing: 1) the original text; 2) the working involved in the conversion to a higher number of decimal places; and 3) any other conversions that may have been possible due to cultural or other ambiguities.

If the user deems the default conversion to be inappropriate, a popup menu will also allow the selection of an alternate conversion or reversion to the original text.

The Metrication add-on attempts to provide "appropriate metric units" by varying the output unit on the scale of the output value and not be fixed to the input unit. For example, "40 miles" will be represented as "64.4 kilometres" whereas "⅛ miles" will be represented as "201 metres". This scaling can also be limited so that values like "30,000 feet" will be represented as "9,144 metres" in line with convention.

Scaling is also applied to decimal places as output values increase. As previously stated, "40 miles" will be represented as "64.4 kilometres" however, "200 miles" will be represented as "322 kilometres" and not as "321.868 kilometres".

The Metrication add-on will detect both full unit names like "feet" and abbreviated unit names like "ft". The add-on will use full names or abbreviated names in its output depending upon which is detected in the input. For example: "40 mi." will be converted to "64.4 km.". This can lead to some false positives: for example, the abbreviation for "font point size" is "pt" however, this could also be seen as an attempt to abbreviate "pint". The popup will explain the conversion used and hopefully the context will reveal that there is no such text size as "5.7 l" (litres).

The Metrication add-on recognises fractions in two distinct ways: 1) Unicode characters expressing fractions, for example "⅘" is Unicode character 8536 (decimal, 2158 in hexadecimal); and 2) textual representation of fractions using numerals, spaces and slashes, for example "4 1/2". There are also Unicode representations of superscript and subscript numerals, for example "⁶" (Unicode 8310 decimal) and "₆" (Unicode 8326 decimal) that are interpreted as numerators and denominators accordingly when separated by a slash.