The knob component comes from GitHub - kramer99/vue-knob-control: A rotary knob control for Vue.js . You can see in that doc there is a value-display-function option that will convert the displayed value. If you’re using any of the 3.4 releases then your widgets should be able to use the arrow function syntax to define a function that satisfies this property.
Start here Creating Personal Widgets | openHAB . There are some explanations of how most of these components are derived and some links to the docs page and f7 pages that cover what you’re looking for.