PCO stands for Potential Change Order (construction management). Suggest new definition. This definition appears somewhat frequently and is found in the following Acronym Finder categories: 1  Business, finance, etc.
Quick Answer. The Roman numeral XIX is the number 19. X is the number 10, and I is the number one. When a lower number is placed in front of a larger number, it indicates subtraction; IX is the same as 10 minus one, which equals nine. The Ancient Romans used different letters to represent numbers.
The numbers range from 13 to 22, from bottom to top. The numeric system represented by Roman numerals originated in ancient Rome and remained the usual way of writing numbers throughout Europe well into the Late Middle Ages. Numbers in this system are represented by combinations of letters from the Latin alphabet.