Most manifold pressure gauges I use start at 10"Hg.
One day you might have a physics type person as a student, who wouldn't believe you about there being a vacuum, because strictly speaking there isn't. Even the words partial vacuum are a bit misleading, in my view you either have a vacuum (and are probably in outer space) or you don't, even though my dictionary has a definition of partial vacuum....(like my hoover when there is too much dog hair in the filter.)
Similarly I think it's important to talk of lower than ambient pressure when teaching about lift. I have heard people describing a vacuum above the wing.
*Visions of a Warrior shooting upwards at escape velocity......*