I'm looking at an object, sometimes very close, to check visual heights. I'm in orthographic view, straight front.
Now I want to rotate slowly to the left/right side, without leaving the xy-plane (while constructing, not for animation). But every slightest move of the mouse kicks me into space, and I can't check exactly. I know rotating while pressing alt key. But this is very crude snapping. I need to rotate smoothly or at least in about 5° steps. I'd like to press Z key, and then keeping movement always stable in xy-plane (like on grap or rotate). It also could help on other axes, or even local coordinates. How can this be done?