Donald Trump raised his right hand while placing his left hand on the Bible Monday afternoon. He then took the oath of office and was sworn in as the 47th President of the United States.

The tradition of swearing the oath of office on a Bible stretches back to George Washington, but not all presidents have observed it.

Legally speaking, it doesn't matter whether the U.S. president placed his hand on a bible. And he wouldn't be the first not to.