Amount of crystals: just enough to half cover the bottom of the lid.
Diameter of the lid is 5cms
Height of the lid is 4.5cms
Only fill to about half way with warm water. Allow the crystals to dissolve. Use a cotton bud to apply the solution to the dial by gently rubbing it across the dial. This is enough to do several dials.
However, as a word of caution, using this method will not be suitable for all dials just those with particular paint finishes. There is no guarantee that the numeral or minute markings will not be affected by such cleaning. It will all depend on the original paint, how it was applied at the factory and how the markings were applied. For example, markings that were applied using transfers will probably not be suitable for this method.