Using xScope with Multiple Monitors in Mavericks and Yosemite (OS 10.9 and 10.10)
xScope doesn't work when using it across multiple monitors on OS 10.9 or 10.10. How can I work around this?
OS 10.9, or Mavericks, introduced a different way of working with multiple spaces on multiple monitors. Because of this, there are a number of issues in xScope, such as displaying guides and frames across displays.
We're currently investigating whether there's anything further we can do to change how displays are handled behavior-wise in Mavericks, but for now there is only one workaround for this issue. In your computer's System Preferences, under Mission Control, you can uncheck the "Displays have separate Spaces" option. Once you do this, you can log out, log back in, and turn on the "Display guides and frames on: All Displays" option in xScope's settings.