On British election night television, a big pointer or dial on the screen that shows which way voters are moving — away from one party and towards another. The presenter pushes the needle left or right and says, "if the swing is this big, this many seats change hands." The key idea is "swing": in British election talk, swing is not how many votes a party got, but how much the vote has MOVED since last time. A party can still lose and have a good swing. The swingometer is simply a picture of that movement, made so that people watching at home can see it at a glance. This is a very British word, and really a television word. You will meet it if you watch BBC election coverage or read British news; you will almost never need to say it yourself. People sometimes use it lightly for any device that shows which way things are leaning — "the office swingometer" for who is winning an argument — but that is a joke built on the real thing.

（英國選舉開票節目上的）選票擺盪指針、擺動計。就是電視上那個左右轉的大指針，顯示選票比上次選舉往哪一邊移動。台灣選舉沒有這個道具，所以沒有固定譯名，多半直接描述。