While they're not all that common nowadays, software developers used to use paper and a writing implement to visualise the flow of their software.
You can do this as a 'big picture', or to draft individual functions.
It helps recognise scope, overlap and optimisation of your logic.
Of course it's not nearly as much fun as wasting hours, days or weeks - and pissing off forum regulars that answer exactly the same questions on a weekly basis.
The pen & paper flow diagram works in a similar way to the original word processor.
It doesn't need batteries, and includes NVRAM to store the most recent changes.