Client impersonation is recognized by an access control service using servicer credentials to allow a servicer to impersonate a user’s context while requesting actions be performed on a computing resource. The system includes a camera having two rotational degrees of freedom, a display, and a combination of switches for routing the video signal. The present invention thus amounts to a computation entirely in the projection domain. The spacer may be formed of a silicon. The flow sensing apparatus includes a flow-responsive element projecting into the fluid flow path, and a position sensor which detects the degree and direction of any change in position of the flow responsive element in response to the fluid flow.