Vacuum Pump Pressure Reading

84 300D Turbo Diesel

Just bought myself a vacuum gauge and testing it. I took a line off the main supply (off the fat one that goes to the brake booster) and hooked up the gauge. At ide it reads 24 inches and no change at higher rpm (means that the diaphram is good). 18 to 21 inches I read is the normal pressure, is mine set too high and should it be adjusted?

I don't think I have any vacuum problem at this time as I can lock and unlock all doors 4 to 5 times.

Thank you for your expert advise.

At the booster line I get about 11-14 inches. It drops as throttle is increased to 0 inches at full throttle. The vacuum valve on the IP creates a "controlled leak" for the transmission, just like a gasser intake manifold looses vacuum with increased throttle.