Yeah it's way too vague.

This morning: (new chat) 42 seconds of thinking, 20 lines of code changed in 4 files = 5% usage

Last night: 25 minutes of thinking, 150 lines of code generated in 10 new files = 7% usage

I think the first message consumes disproportionately much percentage because it's not cached and includes the system prompt, tools, etc.