To develop a rhythm/become good at something. Can be used to describe a physical or mental activity.
The most likely source of this expression traces it to being a reference to the pendulum of a clock, which swings evenly and repetitively. In which case it could date back as far as the 17th century (Christian Huygens, a Dutch scientist, made the first pendulum clock in 1656).
An early use of the expression is found in "Life and Letters" (1864) by English biologist Thomas Huxley.
Judge rules unused Borders gift cards to be worthless(May 23 2013) Borders owes nothing to holders of roughly $210.5 million of gift cards that had not been used by the time the bookstore chain shut down, a Manhattan federal...