Each unit number has 3 digits that denote what building it is in, which floor it is on and where it is located on that floor. The first digit of the unit number is the building. The second digit is the floor and the third digit is the location on that floor. While standing at the entrance of each building, the units would start at the left with zero and numbered consecutively thru nine which is the last unit on the right (example: unit 452 would be building 4, fifth floor, and third unit from the left end of the building).