Licences
Interval reads your dive computer because other people did the hard part first. This page names their work.
libdivecomputer
Dive computer support by libdivecomputer, licensed under the GNU LGPL v2.1.
An open source library that speaks the transfer protocols of around 200 dive computers. The licence text, the full list of supported models and the source are all at libdivecomputer.org.
Typefaces
Interval uses the system typeface on every platform it runs on. This website sets its figures in Source Serif 4, under the SIL Open Font Licence, and its text in Inter where that is installed, falling back to your system's interface typeface.