Quickly calculate the recording interval needed to turn a period of real time into timelapse time.

I shoot a lot of timelapse video and have always been flustered with the mental gymnastics I have to jump through to answer one of the first questions that pops into my mind when I’m first setting up the recording.
“What recording interval, in frames per second, do I need to use to compress a period of realtime into video time when played back at a particular frame rate?”
Me setting up a timelapse recording
Timelapse Calc answers that question with just a few taps in an easy to understand question-answer format.