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.
Roman numerals are the letters that ancient Romans used as their numbers. It is thought that the numerals derived from tally marks, being scratched lines used to keep count. We use tally marks by counting four lines, and then crossing the first four with another line, going diagonally crosswise, like so: