02-4 is a mechanic (level 4) and O is an operator.
Operation classes are divided into different levels from low to high: 0 1, 02, 03, 04, 05. 02 stands for mechanic, 02- 1 is a mechanic (level 1), 02-2 is a mechanic (level 2), 02-3 is a mechanic (level 3) and 02-4 is a mechanic (level 4).