# Paris line

Physical unit
Unit name Paris line
Unit symbol ${\ displaystyle \ mathrm {{} ^ {\ prime \ prime \ prime}}}$
Physical quantity (s) length
Formula symbol ${\ displaystyle l}$
dimension ${\ displaystyle {\ mathsf {L}}}$
In SI units ${\ displaystyle \ mathrm {1 ^ {\ prime \ prime \ prime} = 2 {,} 2558 ... \; mm}}$
Derived from inch

The Parisian line is an old measure of length that was used as a reference unit across Europe in the 17th to 19th centuries .

## definition

The "Paris line" is derived from the "Paris foot" in the duodecimal system .

symbol unit Length in mm
(rounded)
divides into
1' Parisian foot (pied) 324.840 12 Paris inches (pouces)
1'' Paris Customs (pouce) 027.070 12 Parisian lines (lignes)
1''' Paris line (ligne) 002.256 12 scruples (douzièmes)
1'''' Scruples (douzième) 000.188

In 1799 the original meter was set to 443,296 Parisian lines. This means that a Paris line is around 2.2558 mm long.

For a long time in the 19th century, the Paris line and the meter were used in parallel as a reference unit for local linear measurements. The problem with all conversions is the large, unwieldy prime factor 1979, which appears in the sequence of digits 443296. 443296 = 2 5 x 7 x 1979. Rounding from 443.296 to 443.3 results in the prime factors 11 × 13 × 31, ie no common prime factor for the unrounded sequence of digits 443296. Often, rounded values ​​were used for further calculations, which led to error propagation. Therefore, depending on the source, there are significant variations in many historical units.

## use

This reference measure was used in science, e.g. B. Newton , watchmakers , typesetters , opticians and in historical metrology .