Bridge should be perpendicular to what?

[deepbrew]

I just upgraded the bridge on my MK to a Sullivan. Everything went with the fitting and slotting, but the saddle is pitching toward the nu a bit. Is this OK or should it be perpendicular to top? It doesn't seem to be too high (adjustment-wise).

[sunburst]

It should be perpendicular to the top.
In fact, it should be perpendicular to a line tangent to the arch of the top. Some people feel it should lean back toward the tailpiece a little.

[Greenmando]

But it may not be square to the strings. The treble side seems to be closer to the nut to get the right pitch.
My wife's arch top guitar had the bridge tilting toward the nut, I backed off the string tension and tweaked it back. No problem since.

[Michael Lewis]

I feel the bridge should lean back a bit, to nearly bisect the break angle of the strings. Otherwise it has a tendency to creep forward and lean toward the fingerboard. If this is allowed to progress it will fall down and the tension of the strings will slap it into the top, potentially causing damage. Each time you tighten strings the top of the bridge has a tendency to creep forward, so you have to keep an eye on it.