It came to my attention recently (i.e. a few minutes ago) that the panel system seems to set the tooltip units to either DEFAULT or METRIC, never ENGLISH. It looks like the EnglishId for a tooltip in an XML gauge never gets used. It looks like this behavior was introduced in FS9, but I'll leave double-checking that in-game as an exercise to the reader. ; )
I would expect that the behavior would be something like this:
- The tooltip will display the English version if U.S. units are selected by the user in the Settings -> General dialog; the metric version if metric units are selected.
- DefaultID should be a fallback used when the user has selected a units that the gauge didn't specify. For example, if the user specifies a DefaultId and EnglishId but no metric ID and the user has selected metric units, then we should display the DefaultId tooltip.
- If a user chooses a unit for which no tooltip ID has been specified, and no default was specified, then no tooltip is displayed.
Having said this, I suppose I should look into fixing this for a future release. :)
Also of note: HelpId is a default (fallback) that is displayed if no tooltip is specified.