Market Depth shows the complete market depth of both buy and sell queue.
It is useful to track the movement of both the buy and sell queue at different queue levels in the Market Depth to estimate where the daily support and resistance level of the stock is. A price level that has the most volume in the buy queue would indicate a support level. This indicates there are buyers waiting for the share price to drop to a particular level before buying.
The first level of the Market Depth shows the volume both on the buy and sell queue waiting to be transacted. When there is a transaction or when a queue is withdrawn, the volume on that price level will change to reflect the remaining volume queued.