The OSTC 2N is a good dive computer, even if you're dives aren't to 80-90 meters. I use it on all my dives, even the ones that's only to a couple of meters.
Anyhow, I would recommend that you use the configure dive computer feature in Subsurface. I think its the best tool out there, but I'm a bit bias =)
You can read about it in the manual: