TouchRuler

TouchRuler comes with an on-screen 20 centimetre ruler, and a 12 centimetre ruler for your MacBook Pro's Touch Bar. Plus, with TouchRuler mini, you can add your ruler to your Notification Center so you can drag it out to your desktop or full-screen app at any time, allowing you to measure on the fly.

Just like a real ruler, TouchRuler shows the centimetre values beneath the tick marks in large text, allowing you to make a measurement at a glance. You can also use the Click Pad to grab an exact measurement and copy it to your clipboard in a flash, with a simple click on the ruler.

TouchRuler automatically calibrates based on your display's information, so you don't have to deal with an annoying first-time set-up. You can also adjust it manually later.

You can customise TouchRuler and TouchRuler mini with any of four themes; Minimalistic, Classic, Warm, & Cool. You can also make the ruler transparent to easily measure on-screen elements, and make it float above all other windows on your desktop.

TouchRuler is great for designers, architects, students, scientists, mathematicians, and the rest of us who just need a ruler available to access wherever we are, and you can grab it on the Mac App Store for less than the price of a physical ruler (one that doesn't have all the cool tricks TouchRuler has!), at just $0.99USD!