Head loss in 610.8(2) vs. A104.2

[AnnDee4444]

Both of the below code sections are from the 2016 California Plumbing Code. They can't seem to decide how much psi to subtract for elevation gain. Anyone have any insight on this?

610.8 Size of Meter and Building Supply Pipe Using Table 610.4
(2): Add or subtract depending on positive or negative elevation change, 1/2 psi (3.4 kPa) for each foot (305 mm) of difference in elevation between such source of supply and the highest water supply outlet in the building or on the premises.

A104.2 Elevation.
Determine the elevation of the highest fixture or group of fixtures above the water (street) main. Multiply this difference in elevation by 0.43. The result is the loss in static pressure in psi (kPa).

 

[Paul Sweet]

0.43 is correct. 1/2 is probably a rounded number, since it's easier for most people to divide by 2 than multiply by 0.43 in their heads.

 

[Builder Bob]

.5 is rule of thumb, ,4333 is the correct scientific number for calculations - for water pressure loss for each foot of elevation.