18" Pica scale
 
A Pica type scale in typography is a traditional unit of measurement where 1 Pica equals 12 Points, and approximately 6 Picas make an inch, used primarily for measuring column widths, leading (line spacing), and other fixed horizontal elements in print, with digital tools now offering visual scales (like Major/Minor Thirds) for harmonious font sizing, but Pica itself is about physical page layout. 
Key Aspects of the Pica Scale