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.
1 Do not subtract a number from one that is more than 10 times greater (that is, you can subtract 1 from 10 [IX] but not 1 from 20âthere is no such number as IXX.) For 99, do NOT write IC (C â I or 100 - 1).2  DO write XCIX (XC + IX or 90 + 9).here are four basic principles for reading and writing Roman numerals: 1  1. 2  A letter repeats its value that many times (XXX = 30, CC = 200, etc.). 3  A letter can only be repeated three times. 4  2.