Here's a webpage with some suggestions about the origins of this phrase: http://www.phrases.org.uk/meanings/to-a-t.html You may find it interesting - or not. Or it may confuse you even more. But don't worry. Most native English speakers don't know or care about the origins of our idioms. The source and original meanings of idiomatic expressions don't actually matter very much. What matters is how we use the phrases, not what they literally mean. Many idioms don't mean anything at all, and you shouldn't worry about it. The best way to deal with idiomatic language is simply to accept it as it is.

got it. thank you su.ki.