I'm a little bit confused about stem angles and could use some clarification.

I currentlty have an ITM Visia stem with 80° angle- that puts it almost horizontal on my bike. I like horizontal.

I'm considering getting an FSA stem and they state their stems are angled 6°. Does this mean that the it's really 84° in comparison to the ITM (90° - 6° = 84°?) If so, then the FSA stem will be angled up slightly, correct? I don't want that.

Why can't all the manufactures use the same reference point? It would be less confusing.