The calipers on the edges of the ruler are useful when aligning the ruler with the screen element you want to measure. The calipers can be configured on either side or even be turned off completely. Use the L key to cycle through the configurations.

Below you can see the calipers for the horizontal and vertical rulers.

Switching Units

The Ruler can be used to measure in multiple units. The default unit is points (pt) but you can easily switch to inches (in), centimeters (cm), millimeters (mm) or even picas (p) with the ~ (Tilde) key.

Below you can see the same measurement in multiple units.

Tip You can also switch to any of the units quickly with the handy popup. Just right-click on the Unit button to see the popup. You can also set a ruler length manually over here.