barometer
noun [ C ]
uk/bəˈrɒmɪtər/ ussomething that is a sign of how a particular situation is developing, or how people's opinions on a particular matter are changing:
The Philippine Stock Exchange composite index is a group of 30 companies that is the market's main barometer.
barometer for sth The sales of this retail chain are seen as a barometer for consumer confidence across the country.