Can anyone guide me for how to perform the leak test for positive pressure isolator used in sterile area?

I can understand the formula mentioned in ISO 10648-2 for Pressure change method i.e.

hourly leak rate, Tf = 60/t X (pnt1/p1tn - 1)

where,

t is the duration of the test in minutes,

p1 is the absolute pressure (ambient pressure minus under pressure) at the first reading in pascals

pn is the absolute pressure at the last reading in pascals

T1 is the temperature at the first reading in kelvins

Tn is the temperature at the last reading in kelvins

60 represents the 60 minutes in an hour

But for positive pressure what formula we can use?