[zamadatix]

CPU usage calculation can be (mainly) broken down into "percentage time spent not idle due to program" vs "percentage of max performance used by program". The former is usually what an end user cares about and measures the amount a program is hogging the system. The latter is usually what a programmer wants to know to see how optimized the program is.

Both are extremely complex with a lot of nuance after that but the "percentage time spent not idle due to program" type this article refers to tends to be simpler than trying to figure out cache/mode switches/instruction level parallelism/instructions per clock per type/and so on on top of everything you need to figure out in the first case anyways.