thats the gap covered, page-5

When you buy a share, it takes 3 days for the money to be taken from your account. Just as if you sell it takes 3 days for the money to be credited into your account.

If you sell before those 3 days elapse you wouldn't have paid a cent yet you owned the right to the profit or the loss over those 1-3 days. It is risky but can work a treat when announcements are pending or a significant bullish signal in a sector emerges (eg a big uranium price rise).