Hey Ryan,

that is a great question, people are a bit confused about that one — probably it deserves a section in the post. But for now let me give an example (is Kotlin ok?) :

Observable.fromCallable { 1 }
  .flatMap { Observable.fromCallable { 2 }.subscribeOn(Schedulers.newThread()) }
  .subscribeOn(Schedulers.computation())
  .subscribe { Log.e("LOG", it.toString()) }

Returning number 1 is done on computation scheduler.

Returning number 2 inside of flatMap will happen on newThread scheduler, which makes sense as subscribeOn says to use the given scheduler when the fromCallable { 2 } starts. If we wouldn’t put subscribeOn with newThread then it would use the current one (computation ).

So in the end the logging inside subscribe will happen on newThread scheduler.

Does it answer your question?