This is a clay shrinkage ruler, designed to allow you to measure shrinkage with calipers at various stages of the firing. This ruler allows room for the clay type and the sample number.
Giving credit, this is remixed from the following file.
https://www.printables.com/model/1146840-shrinkage-ruler-stamp-for-ceramics
The original creator has the remix options turned off for their model.
The author marked this model as their own original creation.