Adjacent, with respect to a control, telltale or indicator, and its identifier means:
Common space means an area on which more than one telltale, indicator, identifier, or other message may be displayed, but not simultaneously.
Control means the hand-operated part of a device that enables the driver to change the state or functioning of the vehicle or a vehicle subsystem.
Indicator means a device that shows the magnitude of the physical characteristics that the instrument is designed to sense.
Identifier means a symbol, word, or words used to identify a control, telltale, or indicator.
Multi-function control means a control through which the driver may select, and affect the operation of, more than one vehicle function.
Multi-task display means a display on which more than one message can be shown simultaneously.
Telltale means an optical signal that, when illuminated, indicates the actuation of a device, a correct or improper functioning or condition, or a failure to function.
Example 1. A slide lever controls the temperature of the air in the vehicle heating system over a continuous range, from no heat to maximum heat. Since the control regulates a single function over a quantitative range, only the extreme positions require identification.
Example 2. A switch has three positions, for heat, defrost, and air conditioning. Since each position regulates a different function, each position must be identified.
49 C.F.R. §571.101