Erlang can be tricky, so documentation is a must, but when you're 30,000 feet high in an airplane with no internet you might regret not having downloaded DashApp and with it all the Erlang documentation.
But it was on your machine the whole time! You have access to all the Erlang documentation with
erl -man used like so:
erl -man calendar
Which pops open a man page for the calendar module.
When you are learning Erlang the docs are at your fingertips.