However:
$$
h = \frac {\Delta p}{d g} \times 1 4 4
$$
where $ \Delta p $ is the pressure difference across the opening (psi) and $ d_{g} $ is density of lifting gas (lb./ft. $ ^{3} $ ). Combining equation (2) and equation (3):
$$
Q \propto \sqrt {\frac {\Delta p}{d _ {g}}}
$$
The pressure difference across any given opening can be evaluated in terms of: height above a known point of zero pressure difference; rate of pressure change with altitude of the atmosphere (which, for any small section of altitude is assumed to be constant); and ratio of the densities of air and the lifting gas. Since the pressure difference across the appendix opening is zero this is our reference point for evaluating height. Figure 23 shows this pressure relationship in graphic form.
Figure 23. Pressure difference across balloon.