Changing Ruler Units November 16, 2016. Posted in: Tip Of The Day. To change Ruler units, double click on the ruler to display the Units & Rulers preferences dialog box, or right mouse click on the ruler area to select a unit. « Previous Photoshop Tip: | Next Photoshop Tip: » Get The Tip of The Day in Your Inbox! Sign-up for the PTC Newsletter to receive a weekly re-cap of the Tips of The Day. That way you'll never miss a tip. You'll also get instant access to the Subscriber Only Tutorials! Enter your email below to sign up! Your Email Address: You Can Also Get Daily Tips On Your Feed! Every Photoshop Tip of The Day is posted in our Facebook & Google Plus, Twitter, LinkedIn, and Pinterest pages.