measuring eng vavuum

[jocko]

Edit - sorry, meant VACUUM, not vavuum (how many people are gonna click on this link to see an engine "vavuum"!!!

Ok, dumb question, but chasing eng vac on my truck (just ordered a booster and master cyl and THEN measured vac... I know, wrong order) Assumed I had decent vacuum, truck idles and runs fine, under load or not under load, stock cam, etc.

Measured vac by disconnecting the vac line from the carb and putting the vac gauge on in it's place where the distrib vac advance was attached. At idle, read zero vacuum. Vac increased as rpm increased, as you'd expect though.

I've read in several places where 17+" Hg is required to operate a brake booster properly, but never assumed I didn't have the minimum because I have a stock cam. Is the vacuum measured at idle rpm for this 17" comparison or at a specific rpm? I "thought" it was supposed to be a measurement at idle... Does air cleaner being installed/not installed make a difference?

Odd situation, really surprised me. Maybe I won't need that booster after all...

So, either -
i'm somehow measuring wrong
have a bad gauge(?) - but it did increase vac as I increased rpm... (went from 0 to about 18" Hg when accelerating rpm from idle up to about 2500 rpm) (is that backwards - should vac decrease as rpm increases?? maybe the gauge IS bad!)
i actually have zero vac at idle(!)
i have a massive vac leak
or this vac port is restricted/clogged, yada yada

Ideas? - feels like I'm missing something simple. Thanks for your help.

Was gonna fiddle with it a bit, but hobbling around on crutches right now and figured I'd just ask before I bust my other ankle hobbling around the garage...