WOODTURNING TIPS -
A Way to Measure Bottom Thickness

This is a home made caliper, although they are commercially available.
They work by sliding the dowel down into the vessel and
reading the remaining distance at the top of the caliper.
This distance is how thick the material is at that point.
In this picture you can see the top sticking out about 5/8".

Here you can see the caliper placed inside the jaws of the chuck
to get the measurement of the bottom of the bowl.
Regular double ended calipers would probably work on a bowl this size,
but for taller vases this home made caliper is just the thing.