Oath of office of the president of the United States

The oath of office of the president of the United States is an oath that the president takes as he takes office. The chief justice gives the oath to the president of the United States. 
The oath is ordered by the United States Constitution (Article II, Section One, Clause 8), and is given before the president begins his term of office. 
This is what the oath says:
It is unknown how many presidents used a Bible or added the words "So help me God" at the end of the oath, or in their acceptance of the oath, as neither is required by law.