A meter rod may not fit cross-wise inside a breaker (whatever that is).
Assuming it is a rod, the difficulty lies in that it can't measure the diameter of the beaker. Unless you were to attempt to find out the Radius/Diameter, then work out the circumference from that.
Internal diameter.
An internal caliper gauge.
The radius of a circle is half the diameter.
Calipers are used to measure the dimension of anarticle. In measuring a section of pipe you would use an inside caliper to give the internal diameter, and an outside caliper to give the external diameter. The difference being the thickness of the pipe wall.
Assuming it is a rod, the difficulty lies in that it can't measure the diameter of the beaker. Unless you were to attempt to find out the Radius/Diameter, then work out the circumference from that.
Internal diameter.
Internal diameter.
An internal caliper gauge.
External diameter, internal diameter, and tooth count.
A vernier caliper
Measure external diameter. (A) Measure internal diameter. (B) Subtract B from A
It is not possible to answer this without more information. However to find the thickness measure the external diameter, measure the internal diameter subtract the internal from the external and that will give you the thickness of the pipe
vernier calliper
To measure the inside diameter of a ring using a vernier caliper, you must use the small jaw or the internal jaw of a vernier caliper.
Calipers measure the internal or external dimensions of something.
There's not much theory involved; you just have to measure it if you want to know it.