Why 10.7 volt input at ‘71 Duster instrument panel?

The Sunpro CP8215 volts gauge is still available at Amazon... Amazon product ASIN B000FJU8I0 The installation varies from one panel to another. It's not exactly easy in any. I've put several in the a-body rally panel, reusing OEM screen and needle but most owners don't bother with the needle swap. The Sunpro is a bit fragile once removed from its can.
There was one member who killed 2 or 3 of them.
I had custom screen decals produced that have to volt scale included on OEM amp gauge screen. The one decal makes that one gauge look newer than others in the pod.