Matt Young wrote:

The flying club that I am in just purchased a second 172, a really nice
plane, new interior and paint and a nearly new STCd 180hp engine.
Anyway, it has a IImorrow (or Apollo?) 2001 NMS GPS installed. It is
not IFR certified, but pages I've found about it online seem to indicate
that it can be. Does anyone know what exactly is the difference between
a certified and non certified install (other than $$$)? What would be
necessary to make it certified for IFR operations?

In addition to the frequency tests mention, the GPS has to display on an
external CDI, there has to be a switch and annunicator to change that
external CDI from VOR/LOC to GPS, and some installations require an external
annunicator for Approach Mode.