What do calipers measure?

Calipers are precision tools commonly used in various fields such as engineering, woodworking, and metalworking to measure the gauge or thickness of materials. They can provide direct readings of inner and outer dimensions, as well as depth, which makes them highly versatile for measuring thickness and other dimensions with great accuracy.

In the context of visual arts, understanding the thickness and gauge of materials can be critical for artists when selecting substrates or determining the dimensions of artwork components. This precision in measurement helps artists create works that exhibit the intended proportions and structural integrity.

The other options involve measurement of different aspects that do not align with the primary function of calipers. For instance, measuring heat, size of rings, or the amount of powdered glass would require different types of tools or instruments designed for those specific purposes. Thus, the correct choice highlights the fundamental capability of calipers in measuring the gauge or thickness of a variety of materials.