Page scales are used to ensure the accuracy of measurements and takeoffs. The page scale must be set before any measurements are taken and, if it is not, Revu will prompt you to set it the first time you try to place a measurement. See Setting Page Scales for more information.

Viewports are zones in a drawing that use a scale different from the page scale. Multiple viewports can be set for a drawing and can be scaled using different units of measure (or even different measurement systems) than the page scale.