Helix angle on Gear

[[Ch...]]

Alright guys, I feel like I should be able to get this easy but I'm struggling.  Still learning the software.  

How can I get this helix angle on this gear?  I've made a line on the gear tooth, and I want the angle back to either the ID or the top plane which is shown.  

 

 

[[Ma...]]

You can make section with a cylinder, so you can have correct line.

But my knowledge about gears is nonexistent. You can create a helix curve ( in Curves menu ), but i don't know how to report that.

I know how helix looks like and how to calculate it, but not for gears - thread is some sort helix too.
I once tried on cnc mill to calculate helix path according to datasheet of mill tool. I ended in distance of circumference over angle.