Italic Angles

I see some typefaces with negative italic angles in their value and it got me confused as to why is that. Could you guys explain that a bit further?

I am not sure I understand what you mean. Can you give an example? Which typeface?

I guess it might be a bug whenever I open an italic .otf font say from the system.

This is the system’s caslon

In my mind the angle should follow the italic slope… right?

Which Caslon are you referring to? OS X’s BigCaslon.ttf does not have an italic. And I couldn’t reproduce this with any of Adobe’s italic Caslons I have installed.

I’m surprised that it reads something besides zero. When importing a font, I believe Glyphs ignores the italic angle set in the font’s CFF and/or post table and always leaves it at zero.

There was a but in the italic angle import. I fixed it.

According to the specs, it seems that the italic angle should be negative.

Glyphs uses a more intuitive clockwise angle measurement but should set all angles in the exported font file according to the OT specs. Does it not do so?