Consider the equations, $\mathrm{P}=\underset{∆\mathrm{s}\to 0}{\mathrm{Lim}}\frac{\mathrm{F}}{∆\mathrm{s}}$ and ${\mathrm{P}}_1-{\mathrm{P}}_2=\mathrm{\rho gz}$. In an elevator accelerating upward

Given.

$\mathrm{P}=\underset{∆\mathrm{s}\to 0}{\mathrm{Lim}}\frac{\mathrm{F}}{∆\mathrm{s}}$

This formula provides the pressure at an point.

This equation won't change if we move up, down, side, beside, or in any other direction. This is constant at all times.

For,  ${\mathrm{P}}_1-{\mathrm{P}}_2=\mathrm{\rho gz}$ :

Elevator's acceleration should be taken into account if the elevator is moving upward or downward with some acceleration. g will become g_eff.

As a result, this equation is invalid and will alter according on the elevator's acceleration.