Definition
An electrical measuring instrument whose scale is stretched across the range of values the pilot most needs to read precisely, while compressing or omitting the rest. In aircraft electrical systems, an expanded-scale voltmeter typically displays only the narrow band around normal bus voltage (for example, roughly 11 to 16 volts on a 14-volt system) so small voltage changes are easy to see.
Plain English
A gauge that zooms in on the part of the scale you actually care about, so small changes near the normal value are easy to notice.
Context Anchor
Seen on aircraft electrical-system gauges, such as a gauge showing battery or generator voltage.
Derivation
‘Expanded’ comes from the Latin expandere, meaning to spread out or stretch. The scale is literally stretched across the useful range so the pilot can read small differences that would be invisible on a normal full-range meter.
Why Pilots Care
It lets the pilot notice small drifts in voltage or current that could signal an impending electrical problem.
Analogy
Like a kitchen thermometer made just for candy-making: instead of showing every temperature from freezing to boiling, it stretches out the narrow range that actually matters, so you can read it at a glance.
Intuition Check
Do not read “expanded-scale” as meaning a bigger instrument. It means a smaller range of readings is spread out so it can be read more clearly.
Example Sentence 1
The expanded-scale voltmeter let the pilot catch the slow voltage drop that warned of a failing alternator.
Example Sentence 2
On preflight the pilot confirmed battery voltage was in the green band on the expanded-scale meter.