To Number or Not To Number

Here's a portion of a display from an iOS app that allows users to connect to a Wireless Valve Control device.

UPDATE: My question is regarding the -42 dBM and 2.97V labels.

As a code implementor, whether to show a number, an analog graphic, or both, has always been kind of "what seems to work best".

When space gets small, icon only is often nice. Icons only here might work, but the numbers add a bit of increased fidelity to the reading and help communicate what the icon is actually describing.

Is there a more rigorous/disciplined approach to when one should include the numeric value of a status value? Other than "that looks best/is nice to have"?