Hi,
Although not specific for this addon, maybe the following helps in understanding how FSX deals with gauges.
This is just generic info, since (IHMO) "An idiots guide to ...." is never the solution.
Because even the slightest copy/paste/typing error leaves you scratching your head because it doesn't work, while you don't have a clue why.
So my suggestion is always to invest some time in grasping "how it works"; sounds complex, but once you get the hang of it, a next time you'll know ...
Here it goes ... (info I posted a few times before)...
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23. About gauges in FSX: types, versions, locations, etc...
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Since there are many questions on gauge types, where to install a gauge, how to deal with gauge versions, etc. here's an explanation.
First of all, the word is spelled "gauge", not "guage"

A very commonly made mistake, causing FSX not to recognise a gauge definition in the panel.cfg file...
Types of gauges
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FSX uses two types of gauges: "C/C++"-compiled gauges (.gau or .dll files) and XML-interpreted gauges (.xml files).
- .gau/.dll files may contain several sub-gauges, and also includes the bitmaps for these gauges.
- .xml files are pure text files using XML-syntax (interpreted by FSX) which refer to external bitmap (.bmp) files.
Multiple .xml gauges plus their bitmaps can be bundled into one .cab file by a MS-tool called Cabdir.exe.
Note that Winzip can extract files from a .cab file, but NOT pack them into a .cab file.
Examples (see the panel.cfg of the default FSX Boeing 737-800)
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gauge00=B737_800!pfd_screen, 189,548
This line refers to the gauge pfd_screen.xml in file B737_800.cab in folder 'FSX'/SimObjects/Airplanes/B737_800/Panel/
gauge00=737-400!Comm 1, 0,159, 68
This line refers to the sub-gauge "Comm 1" in file 737_400.dll in folder 'FSX'/Gauges/
Location of gauge files
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If you specify in the panel.cfg
gauge00=aaa!bbb, ......
With this definition line, FSX tries to find the gauge in the following order of priority.
1. Gauge bbb.xml in folder "FSX"/SimObjects/Airplanes/"youraircraft"/panel/aaa/
2. Gauge bbb.xml inside a file aaa.cab in folder "FSX"/SimObjects/Airplanes/"youraircraft"/panel/
3. Sub-gauge bbb inside a file aaa.gau in folder "FSX"/SimObjects/Airplanes/"youraircraft"/panel/
4. Sub-gauge bbb inside a file aaa.dll in folder "FSX"/SimObjects/Airplanes/"youraircraft"/panel/
5. Gauge bbb.xml in folder "FSX"/Gauges/aaa/
6. Gauge bbb.xml inside a file aaa.cab in folder "FSX"/Gauges/aaa/
7. Sub-gauge bbb inside a file aaa.gau in folder "FSX"/Gauges/
8. Sub-gauge bbb inside a file aaa.dll in folder "FSX"/Gauges/
A few notes
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1. As you can see, with the same panel.cfg definition, you can choose to place your gaugefile either in the main ..\gauges\ or local panel folder.
Avantage of ../gauges/:
- Only one, shared gauge file (saves diskspace)
- Installing a newer version of the gauge, you only have to overwrite one file for all panels using it.
Advantages of the local panel folder:
- Allows for multiple versions of a gauge.
- You never (accidentally) overwrite a gauge with an older version.
- Easy maintenance if you decide to remove a plane with it's panel: you simply delete the whole .../"youraircraft"/ folder (and panel subfolder) without leaving (potentially unused gauges) in the ..\gauges folder; or accidentally delete a gauge that is still used by another aircraft panel.
- Faster loading of the panel, because of the seach order and the size of the gauge folders. Allthough you probably won't notice a difference, unless your main gauges folder contains 10000's of gauges.
So you can decide yourself which "strategy" best suites you.
2. For XML gauges, you can decided to unpack the .cab file (e.g. using WinZip) into a subfolder with the same name as the .cab filename.
Adavantage:
- Easy change/replacement of a single .xml or .bmp file, without bundling/replacing the whole .cab file.
- Much faster loading of the panel with very large .cab files (because the file needs not to be unpacked first)
And these are only the main options and advantages

To name three other possibilities:
1. You can put gauge files into a subfolder of .../gauges/.
E.g.
gauge** = foldername/filename!gaugename, ..,..
when the gauge file is placed in folder ..../gauges/foldername/
Not very usefull given the other options, especially since if it's wasn't setup this way by the designer, you have to modify all gauge definitions in the panel.cfg.
2. Use panel aliasses, i.e. a common panel folder (with gauges) for more aircraft (or aircraft models).
The panel.cfg only needs to contain the line "alias=......", where ..... specifies the path of the actual panel folder (which can be anywhere in the FS tree)
3. Modify the bitmap of an xml gauge for a specific panel.
Suppose you want to adapt the bitmap of an XML gauge in a .cab file, for one specific panel.
What you do: Extract the .bmp file from the filename.cab file, eg. with Winzip, to folder "FSX"/SimObjects/Airplanes/"youraircraft"/panel/filename/ and modify it.
Now this particular panel will use the modified bitmap and NOT the bitmap from the .cab file.
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Hope this clarifies a few things.
:ernae: Rob