Not possible to compare key figure for &

What causes this issue?

There is no key figure that would provide a useful comparison with the
key figure &V1&.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

You cannot compare the chosen key figures.
Choose a different key figure in order to carry out a comparison.

Error message extract from SAP system. Copyright SAP SE.