Caliper vs micrometer

[Edd]

When and why? What does a micrometer do a caliper won't? Do reloaders need both?

I have 4 measuring tools that I use for reloading. If I could only have one, it would be the caliper. I think the order they are listed is the order of their value.

0-6 inch caliper
0-1 inch anvil micrometer
0-1 inch outside micrometer
0-1/2 inch ball face micrometer