Gauge Pressure calculation

Hi can anyone tell me how to calculate gauge pressure @ diffuser outlet . i got some details from the internet. But it is not clear to me.
Here are the details:

pg = ps - patm
where
pg = gauge pressure
ps = system pressure
patm = atmospheric pressure
atm = 1.01325 bar = 101.3 kPa
System pressure = density x gravity x height..

1 :Height indicates... what height? is it floor to diffuser or duct or plenum height?

2 :What is unit of System pressure? ie) density (kg/m3) x gravity (m/s2) x height (m) ..>>>>>>>>>>( result unit is kg/ms2)

3 :For an example i have density of 1.1839 kg/m3 @ 25 deg.c & height 9 mt ( floor to diffuser ) i got this value = 104.52 unit?...is it correct..

4 : If it is correct then the gauge pressure will be =104.52 - 101.3 = 3.22 kpa?.....

any one try to clear this..


Regards,

Giri. J