Graphic Art and Printer's Ruler Information
Most industries and users of measuring rulers utilize either the English or Metric measurement systems.
English: miles, yards, feet and inches (and fractional or decimal values of part of an inch)
Metric: kilometers, meters, centimeters and millimeters (decimal values of part of a millimeter)
The Printing and Graphic Art industries, since the days of Gutenberg (credited as being the father of the printing press) have used a measurement system specific and unique to their industry. The linear measurement system is the Pica and the Point. These industries also used some other units of measure which we will discuss below.
The PICA and POINT
The pica and point are both used for linear measurements and in addition the point is used to specify type height and line weight (thickness).
One Point = 0.0138"
One Pica = 0.1656"
There are 12 Points in a Pica.
Many people like to say that there are 12 points in a Pica and 6 picas in an inch. This is satisfactory for small distances measured but produces significant errors over longer distances.
For example:
Correct Conversion of 6 Pica = 6 x 0.1656" = 0.9936"
At 6 Pica to the inch, 6 Pica = 1"
Error = 0.0064" - not a significant amount
Correct Conversion of 108 Pica = 108 x 0.1656" = 17.8848"
At 6 Pica to the inch, 108 Pica = 18"
Error = 0.1152" – extremely significant, nothing will line up on a printed piece
As can be seen from the examples above, it is not always a good idea to use the formula of 12 Points equals a Pica and 6 Pica in an inch.
Modern computers, graphics programs, drawing programs, etc. will often display and use Picas and Points, however they usually use the straight conversion of 12 points to a pica and 6 pica to the inch. This produces a value of with an ever recurring decimal for both the point = 0.013888888888 .... and the pica = 0.1666666666....
How these programs perform is a product of how the software is written and how distances and round off errors are calculated. The less the number of decimals used after the period and the longer the distance, the higher the potential for significant errors.
THE DESKTOP PUBLISHING PICA AND POINT
This uses the convenient formula of 12 Points to the Pica and 6 Pica to the inch. Please see the discussion above.
When GEI International, Inc. manufactures these measuring scales, we correct for the round off errors every inch and the graduations within each inch are placed to six decimal places. This produces a measuring scale where the errors are so small they cannot be measured.
THE AGATE LINE SCALE
This unit of measure is normally known by the terms Agate or Agates. This is a unit of measure that was historically used to measure the depth (number of lines) of advertising columns in newspapers. There are 14 Agate lines in an inch.