I was actually looking into that one too as I find the altimeter needle to come in rather choppy. A friend of mine tried to help as I don't have any xml code talent at all, but, so far, I could only break the gauge code or the 'update' parameter had no effect at all. I know that you can alter the xml code to allow for a higher refresh rate though.

The MS SDK describes the parameter here. http://msdn.microsoft.com/en-us/library/cc526953.aspx#mozTocId45130

Update Objects
Update objects are used to provide time based updates to a gauge. The GPS system is an example of a complex instrument requiring the use of Update objects.

Frequency      Integer value indicating how often the update should be run, in updates per second. Enter 1 for the slowest frequency of updates (one per second).

Thanks to some help, I now know that the code should look like this.
[code]   <Update id="fastgauge">
    <Frequency>1</Frequency>
  </Update>[/code]
with the number defining the refresh rate per second.

As said, I've tried a bit, but I think I've placed it the wrong way or so. I know that some Airbus flyers used that tweak on another dev's plane and received fluid gauges for trading in a few fps. That's my plan.  :D