Mobile manipulators are being marketed around the world as single manufacturer systems (i.e., robot arm and vehicle manufactured by the same organization) and as independent robot arms, from a different manufacturer and integrated with automatic guided vehicles (AGVs) or mobile robots. Test methods for measuring safety and performance of either of these types of mobile manipulators have yet to be developed and therefore, potential users cannot compare one system to another to match to tasks. Similarly, the control of these systems can vary greatly from AGV control to more autonomous mobile robot control and further, to robot arm control methods. Systems Modeling Language (SysML) is a general-purpose modeling language for systems engineering applications that supports the specification, analysis, design, verification, and validation of simple through complex systems, such as mobile manipulators. This paper uses SysML to describe a method using an artifact for performance measurement of mobile manipulators performing assembly tasks. Uncertainty propagation, a key component in understanding the effects of mobile manipulator constraints, is also modeled and described.