InDesign has a built-in ruler – the Measurement tool that hides behind the Eyedropper. You can use it in a couple of ways.
Select the Measurement tool and draw a line to measure something. The Info palette should open. Your measurement results will appear in the Info palette.
Below, measuring the left side of the magenta box, you can see the length (D1) and the angle. Also note that the width and height of the shape, the coordinates and the colors are also shown in the Info palette. And once you've drawn a measurement line, you can move it around to compare to other shapes.
But that's not all. You may need to measure the angle between two lines. If I want to measure the angle between the pink and black boxes, InDesign has a hidden "protractor" measurement mode. Draw your first line. Then, holding down the option key, draw a second line that starts at the endpoint of the first line. Your cursor should change into a protractor that looks suspiciously like a compass. When you draw both lines, your measurements for the first line (D1), second line (D2) and the angle between them is shown.
Oddly, this ruler is more capable than the one in Illustrator where I would use it more often. The Illustrator measurement tool lacks a protractor mode. Seems like it would be an easy addition for them. (And if Adobe really wanted to improve the ruler in their apps, they should take some tips from the type design app, Glyphs, which has an amazingly functional measurement tool.)