Rear hanger location- Sram Fit guide

I am confused by the hanger location per Sram’s Fit guide. Is the off set (X) measured from a line horizontal to the ground (or axles) like the drawing shows or is it 90 degrees from the chain stay centerline?

I 3D printed a centering marker that goes in the derailleur mounting hole and drop a plumb bob off a spot 7-10MM behind the center of the axle then rotate the drop out so the centering pin in the mounting hole aligns with the plumb line.

Looking at this drawing the horizontal line says “To BB Axis” Given the BB drop the horizontal line would actually be angled down making the 90 degrees that measurement X uses would be more like 81 degrees.

I made two drawings. Option 1 is 90 degrees off the CS center line. Option 2 is 90 Degrees off horizontal. I made both have a X value of 9MM but the Derailleur mount hole is located in a different place in space. Can someone help me understand the proper way to clock dropouts?

Measured 90

Option 1 is correct. It is measured relative to the “virtual chainstay”

Virtual Chainstay: the imaginary plane that connects the axle center to BB center.

Great, Thanks! I wish their drawing did not make the chainstay horizontal.

I modified the drawing because my hanger is actually 28Mm.

It looks like I need to drop my plumb line 11.12 MM behind the axle center

Here is how I understand it: