How to calculate if s&p 500 went up or went down

This is probably a stupid question but I need to be sure. I'm a noob and I don't plan to trade, need to know because I'm doing a project.

If I was to calculate if the stock price went up/stayed the same or down on a day, would it be (close - open) or would it be close(current-day) - close(previous-day)

Submitted October 25, 2017 at 05:02AM by phreak121 http://ift.tt/2gHGMSk