I am looking at 1 minute btc/usd graph at https://bitcoinwisdom.com/markets/bitfinex/btcusd . So how do they get last price of bitcoin? Can I see the last completed transactions of bitfinex? I know there is two prices in order book: Bid and Ask. So does it look at the order book to get the last price? Or looks at the last completed transaction?

Thank you.