Thanks you for that, I think I misunderstood the purpose of offsets. With my proposed change then yes, in order to specify a gauge via its centre position then you'd need to add the offsets manually for each gauge.
However, my original thought process, and the thought process of some others that I discussed this with on IRC was that you specify gauge positions based on the top left corner of the gauge, not the centre. And thus the confusion

I guess that the fact that the Origin: values used in the original patch were 0.0, 0.5 & 1.0 added to my confusion, i.e. the offsets didn't seem to be used to provide the position of the top left of the gauge compared to the centre of the gauge.
So, what is easier for the modder? Lets use the 1024x768 FS2 centre reticle (gunsight/crosshairs) as an example.
Defaults coded into FSO:
+Center Reticle:
Origin: (0.5, 0.5)
Offset: (-19, -14)
Example one: move the reticle off centre / ~50 pixels to the left for an Ursa/Rhea like offset firing point, using current code
+Center Reticle:
Offset: (-19, -64)
(assume the modder knows what the default offset is)
Example two: same thing except specify the top left corner position of the gauge and assume the proposed change was added
+Center Reticle:
Origin: (0.487,0.370)
Example three: same as two, except without the proposed change
+Center Reticle:
Origin: (0.487,0.370)
Offset: (0, 0)
Note, I have not tried these using these examples in game.
Is it simply a case of being easier to specify position via centre (current code), or via top left (proposed code)?
It the best solution just knowledge/documentation? (with a better Assertion message?)