Pressure Diagram & Its Law

In the pressure diagram where it shows the pressure gauge above atmospheric and below atmosphermic with reference datum. I've been thinking over and over again because I have heard that there is a positive pressure such 10Pa, 50Pa, 1000Pa etc which is below atmospheric pressure that I will consider it as negative pressure based on the diagram.

How come there can be such positive pressure below atmospheric? If this is wrong then any values below atmospheric is considered negative pressure and vacuum, right?