How do I enable the rulers on Layout Editor?

Seems like the ruler has been removed from the Preview tab of the Layout Inspector since Android Studio 3.0. It's 2020 now and Android Studio 4.0 has a new Layout Validation tool to preview the layout on different devices and display configurations. Not really the same but at least the Layout Inspector seems much more reliable than those days.

More details at: https://developer.android.com/studio/debug/layout-inspector#layout-validation

The Guidelines are the rulers. You move them around to get the measurements you need. Expressed in percentages or units.