A marking menu is designed to allow a user to perform a menu selection by either popping-up a radial (or pie) menu, or by making a straight mark in the direction of the desired menu item without popping-up the menu. Previous evaluations in laboratory settings have shown the potential of marking menus. This paper reports on a case study of user behavior with marking menus in a real work situation. The study demonstrates the following: First, marking menus are used as designed. When users become expert with the menus, marks are used extensively. However, the transition to using marks is not one way. Expert users still switch back to menus to refresh their memory of menu layout. Second, marking is an extremely efficient interaction technique. Using a mark on average was 3.5 times faster than selection using the menu. Finally, design principles can be followed that make menu item/mark associations easier to learn, and interaction efficient.