Definition
The face of an instrument, marked with numbers, graduations, or symbols, against which a pointer or indicator is read to display a measured value.
Plain English
The marked face of a gauge or instrument that you read to see what value it is showing.
Context Anchor
Seen on cockpit instruments such as altimeters, airspeed indicators, pressure gauges, and heading indicators.
Derivation
From the Latin 'dies' meaning 'day,' originally referring to a sundial -- a marked face used to read the position of the sun's shadow. The meaning extended to any marked face used with a pointer to show a measurement.
Why Pilots Care
Pilots must read instrument dials correctly because a wrong reading can lead to poor decisions about altitude, speed, fuel, engine condition, or aircraft direction.
Intuition Check
Do not read dial here as a phone control or only as the act of selecting a setting. In this instrument sense, the dial is the marked face you read.
Example Sentence 1
He set the desired altitude by turning the knob until the number appeared in the window on the dial.
Example Sentence 2
Vibration caused the needle on the fuel quantity dial to flicker during the climb.