All transactions conducted on the exchange are plotted on this chart:
Red circles show sell transactions.
Blue circles show buy transactions.
Green circles appear when the direction of the transaction is undefined. It is used when the exchange does not transmit the direction of a transaction. In this case, the direction is determined based on the price of the transaction as compared to bid and ask prices.
A buy transaction is executed at the ask price or above, a sell transaction is executed at the bid price or lower. The direction is undefined if the price of the transaction is between the bid and the ask.
The larger the circle, the greater the volume of the transaction. Transaction volumes are also shown as a histogram below the tick chart.