The December 2013 version of the QDM has removed references to timing operators and functions. Without these definitions the QDM cannot represent the logic required to express a Clinical Quality Measure. Currently the definitions for timing operators and functions are provided in the Measure Authoring Tool user guide. The user documentation for the tool that allows measure developers to build clinical quality measures is not the ideal location for the definition of these operators and functions. Instead, these definitions should be restored to the QDM providing a gold-source reference for these constructs that the Measure Authoring Tool as well as individual vendors can use to accurately build and implement measure definitions.