How is D9-THC properly numbered and named

Im aware that naming/numbering cyclic compounds is hell, but i remember telling myself by the time I finish my chem minor ill at least understand the structure of household drugs. Well I'm here and still have zero clue how this numbering or naming makes sense. So from my understanding this is a benzochromene derivative but even following that numbering im lost.

Was this named under old iupac rules? Sorry in advance, any advice appreciated

https://thetruthaboutforensicscience.com/wp-content/uploads/2012/01/Delta-9-THC.png