How to use/understand percentage in scripts

From Stereomerger

Since Stereomerger must handle images of many sizes, most filters use percentage to express position and size.

Position

A position of 0% horizontally and 0% vertically is in the upper left corner. Like this:

    0%            100%
  0% ----------------
    |               |
    |               |
    |               |
    |               |
100% --------------- 100%
                  100%

If defined in pairs, like (10,15), the horizontal/X position is always the first value and the vertical/Y position is the second one.

In a VGA image of 640x480 pixels, (10,15) would be translated into pixel position (64,72).

The pixel values are always calculated from the current image size.

Size

A size in percent, is also always calculated from the current size. If you for instance have a VGA-image (640x480) and add a frame with thickness 5%, the width and height will increase with 32 and 24 pixels and result in a 672x504 pixel image. If you choose to add another frame with 5% thickness, the frame thickness in pixels will now be 34 and 25.