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 that we normally use (1, 2, 3 etc) are called Arabic numerals. But we sometimes use another system for writing numbers - Roman numerals. The Romans used letters of the alphabet to represent numbers, and you will occasionally see this system used for page numbers, clock faces, dates of movies etc. Image: On the clockface you see Roman numerals for the hours and Arabic numerals for the minutes.