Measuring angles with the ruler tool
There’s a very good extra use for the ruler tool in Photoshop - apart from the obvious of-course!
When you draw a ‘line’ with the ruler, you can then hold down Alt and draw a new line starting from the end of the first. If you take a look up at your control strip across the top of the screen you will now see an angle measured.
This can be useful if you need to measure and match angles in layered compositions - now you can transform you layers by that angle and they will all match up! Incidentally - if you have a few layers to transform, you can use the ‘transform again’ command under Edit>Transform>Again to quickly apply the same transformation to another layer.