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, the numeric system used in ancient Rome, employs combinations of letters from the Latin alphabet to signify values.rom the 14th century on, Roman numerals began to be replaced in most contexts by more convenient Hindu-Arabic numerals; however, this process was gradual, and the use of Roman numerals in some minor applications continues to this day.