I am shopping for a new stem to match the dimensions of my existing stem -- an IRD A4 road stem. I have seen it advertised as a +5 degree rise. Whatever that is, I want the same rise, which looks slightly higher than flat when flipped.

Other stems I have seen advertise crap like 80 degree rise or 84 degree rise.

Far as I can tell, most head tubes are around 74 degrees, so if a stem is 5 degrees down, I can see how it would be about 80 degrees from vertical, so maybe that is waht they mean, but I don't want to rely on this assumption.

So please explain stem rise.

Thanks!