Allow custom Measurement Scale in Ruler units / Info panel

When setting a custom Measurement Scale [Image > Analysis > Set Measurement Scale], it would be really useful if we can use that new scale for the units in preference to be able to see it in the Ruler and the Info panel.

So, my request is simple: Add a choice in the preference [Units & Rulers] to pick "Custom Measurement Scale". This will allow easy transformation of layers and reading according to a specific scale.