The Scaled Pressure at Altitude 'z' computes impulse using the pressure at the 'z' altitude and the ambient pressure. This equation is part of Sachs scaling law.
In the case of blast waves from explosions produced at altitude, where ambient conditions can be very different from those at sea level, the most commonly used scaling law is that due to Sachs. The application of the Sachs scaling law leads to the formulation of altitude scaling factors.