bugbear wrote:

Given that a surface gauge (and indeed height gauges)
need to sit securely on a surface plate,
why don't they have a tripod support
(which sits secure regardless),
instead of having a flat base, which
is only stable if it's carefully made truly flat?

Three points of contact is a lot more fun to level. I spent a bit of time today to level
4 points of contact on a balancer system.

As far as your question goes, range. A flat surface gage can be used in many more
situations. I've used 1/2" of a machinist square often to square up a part vertically in
a Kurt vise.

Wes