diff -r 1c362eb39bdd -r 5df5b8a103af ThemeFiles.wiki
--- a/ThemeFiles.wiki	Sun Dec 07 17:26:55 2014 +0000
+++ b/ThemeFiles.wiki	Sun Dec 07 17:41:16 2014 +0000
@@ -81,6 +81,18 @@
 === `amGirder.png` ===
 You can create a custom image for manually built girders (from the  “Construction” utility) by adding this file to your theme. Don’t confuse this with `Girder.png`! If unspecified, `Data/Graphics/amGirder.png` is used.
 
+The image is of size 480×480 pixels and consists of 9 sub-images of size 160×160 each in a 3×3 grid, but only 8 sub-images are used. This table shows the starting and ending coordinates of the squares which make the sub-images:
+
+|| *x minimum* || *y minimum* || *x maximum* || *y maximum* || *Orientation* || *Length* ||
+|| 0 || 0 || 160 || 160 || Horizontal || Short ||
+|| 0 || 160 || 160 || 320 || Falling right || Short ||
+|| 0 || 320 || 160 || 480 || Vertical || Short ||
+|| 160 || 0 || 320 || 160 || Rising right || Short ||
+|| 160 || 160 || 320 || 320 || Horizontal || Long ||
+|| 160 || 320 || 320 || 480 || Falling right || Long ||
+|| 320 || 0 || 480 || 160 || Vertical || Long ||
+|| 320 || 160 || 480 || 320 || Rising right || Long ||
+
 === `Snowball.png` ===
 This is the image of the mudball when thrown. It has a size of 16×16 pixels. By default, `Data/Graphics/Snowball.png` is used.