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.
When a lower-value number precedes a higher-value number, the lower-value number is subtracted from the higher-value number. The Roman numeral for 47 is written by breaking the number down into 40 + 7. The number 40 is written as XL, which is equal to 50 - 10, since four 10s in succession is not allowed. The number seven is written as VII, which is 5 + 2.