An endless belt tensioner system adapted to apply a tensioning force on a ground-contacting endless belt of a vehicle is provided, the tensioning force being substantially proportional to an endless belt drive force applied to the endless belt to move the vehicle. In one or more embodiments, the enclosure includes a modular housing that is configured to be gangable with one or more other housings to provide a range of sizes and configurations. Preferably, the thin plate is formed of a material having a nonlinear optical effect or an electro-optical effect. The query response is sent back from the second SCP to the originating SSP without passing through the first SCP. The indication device indicates when a command has been received and indicates when the command is being utilized to control the external infusion device so that the external infusion device is capable of being concealed from view when being remotely commanded.