Ubiquitous technologies are changing our lives.We are becoming more connected and able to conduct our computing tasks anywhere at anytime from any device.Vertical interaction with an individual interactive system is no longer the only way to achieve tasks.Currently, users can interact horizontally with multiple user interfaces to achieve their tasks.This has created a need for measuring usability of multiple interactive systems, concerning users horizontal interaction beside their vertical interaction.In this paper, we surveyed the actual meanings and interpretations of usability and its attributes across several standards and models.We found that the existing usability standards and models do not consider horizontal usability aspects.Therefore, taking into consideration the characteristics of user interaction with multiple interactive systems, a hierarchical model, which is called Cross-Platform Usability Measurement (CPUM), has been developed.This model decomposes cross-platform usability into 12 factors.These factors were further decomposed into measurable criteria, and finally into specific metrics.