Nine instruments. Six take numbers you already have and give you the ones you do not; two read live outdoor conditions for wherever you are; one prints. They all share an implementation, so no two of them can disagree with each other or with the app.

What none of them do is measure the room you are standing in. No phone has a humidity sensor and neither does a browser — the live pages read an outdoor weather service, and the rest work from figures you type in. Where the numbers come from is the longer version of that answer.