The manual says:
● To specify which unit to show on the rulers, open the Zoom pop-up menu and select one of the options. You can choose between points, inches, and centimeters.
● To hide the rulers, select Off. To display the ruler again, open the pop-up menu above the scrollbar at the far right and select one of the units.
(Cubase_Pro_Score_12_Score_Layout_and_Printing_en.pdf — WebHelp Version)
I think the two marked in bold texts should be replaced with: open the Zoom pop-up menu located above the scrollbar at the far right.