All spot transactions made on binance are saved, together with their amount and whether they are a buyer or seller.
The difference between the sum of buyers and the sum of sellers for a certain time period is shown in the chart.
For example; If the buy order takes place as a market maker with a volume of 1,000 btc for 1 hour, and if the sell order takes place as a market maker with a volume of 500 btc for the same hour, it will appear as a 500 btc buyer in the graph.