A barometer is an instrument that measures air pressure and shows when the weather is changing.
N-COUNT
變化的標志；晴雨表
If something is a barometer of a particular situation, it indicates how things are changing or how things are likely to develop.
例句
In past presidential elections, Missouri has been a barometer of the rest of the country...在過去的總統選舉中，密蘇里州一直是國內其他州的晴雨表。Our sleep pattern is a barometer to our psychological well-being.我們的睡眠模式是心理健康的晴雨表。