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.
Thus: I = 1 V = 5 X = 10 L = 50 C = 100 D = 500 M = 1000 Numbers are presented by combining these values and adding them together. Thus the Roman numeral VI represents 6. That is, V + I = 5 + 1 = 6. Roman numerals are normally written from left to right, with the largest value first.