diff --git a/UrumbotXY/README.md b/UrumbotXY/README.md
index 45060a0d43a737039724efd380049f3bdcc7dd6f..2c680594a9d2b8d9f4ef115aaeb7746d9835b0f8 100644
--- a/UrumbotXY/README.md
+++ b/UrumbotXY/README.md
@@ -79,7 +79,9 @@ Closeup of traces:  Using 1/64" bit and 0.8 mm horizontal separation of paths, a
 
 This machine is close to being able to mill circuitboards.  For the first try, the stiffness of the end effector wrt sideways force seems to be the limiting factor, rather than the xy stiffness.  Next step: a better arrangement of z-stage and full incorporation of the z-motion into the software.
 
-Small-excursion z-axis design:
+### Small-excursion z-axis design:
+
+A cam translates the spindle by flexing the beam a few mm.  Total excursion at the spindle is about +/- 2 mm.
 
 <img src=img/fixed_z.jpg width=50%><br>
 <img src=img/z-cam.jpg width=50%><br>