hi there...
here it is:

the start point is where you first click to start dragging out the selection box (in this case, pixel 500x, 100y)
the end point is where your selection ends (pixel 1000x, 200y)
which is equal to a box size of 500 width by 100 height
ad thus has a ratio of 5,000 to 1,000 (box is 5 times wider than it's high) this ratio is for the relation between x and y, where y remains a constant (1,000)
that's pretty much it
what you want to put in te panel.cfg is, in the following order, the starting point x, y coordinates(top left corner of gauge),then width, and height
in this case it would look like this:
gaugexx=gaugename, 500, 100, 500, 100
c ya
Moach