On the button
Just right; exactly on target or at exactly the right time.
The Vancouver Winter Olympics have provoked a rash of emails asking if 'on the button' derives from the sport of Curling. In curling, which has a Scots sub-language all of its own, the centre of the target (a.k.a. 'house') is called the button. The object is to get the stones as near as possible to the middle of the target, so being 'on the button' at the end of a game is clearly no bad thing.
The sport has an ancient enough pedigree to have spawned the odd phrase as well as its jargon words, as it originated in Scotland in the 1600s and it would be pleasing to find a Scottish phrase that wasn't coined by Sir Walter Scott. Regrettably, 'on the button' is a 20th century phrase and from the USA. It is from a sporting context, but from boxing rather than curling. The 'button' in question is the US slang term for the point of the chin. The phrase started being used around the end of WWI and there are many printed citations of 'the champ was socked on the button' etc. from that period. The earliest citation of the phrase that I have found is from the impressively named Indiana newspaper The Logansport Pharos-Reporter, May 1917:
Moran is a one-punch fighter. He packs a mighty mean crusher in his right hand. If it ever lands on the button Morris will prove himself a superman if he doesn't go down.
The precise location of the button was made clear in Harry Witwer's screenplay for the 1921 boxing film The Leather Pushers:
The Kid floored him with a right cross to the button of the jaw.
P. G. Wodehouse, a frequent visitor to the USA, took up the phrase and introduced it to the UK, as in his novel Laughing Gas, 1936, for example:
He soaked [socked] him on the button, don't you know.
Before long the term began to be used to mean 'accurately; precisely' and came to refer to times as well as locations. An early example of that is found in Printers' Ink Monthly, May 1937:
On the button, a program ending exactly on time.
The interest in the possible curling-related source of 'on the button' has come about because of the media interest in the much-fancied British team and their chances of a gold medal in the Winter Olympics. It's no surprise that, with personnel with names like Ewan MacDonald, David Murdoch etc., the British team is really the Scottish team. That's only so long as they are winning though. Having lost to Sweden, the English newspapers have stopped referring to 'our boys', who can now enjoy being Scottish again.