Besides identifying colors, a frequent use case in the designer to developer hand off process is determining the exact dimensions of elements in a mockup. Whether it’s button sizes or padding values, designers spend a ton of time tediously drawing redlines for measurements. With the new Measurement Tool, that should now be a thing of the past.
The Measurement tool comes in two flavors - the Box Measure and the Line Measure. The Box Measure allows you to measure rectangular elements like buttons. The Line Measure not only measures the direct distance between two points, but also the angle between them and the horizontal.
In the vein of showing being better than telling, you can try out the Measurement Tool here in the Inspector as well as in the File Viewer.