diff --git a/sfc/slicer.py b/sfc/slicer.py
index 3857ff9..8ae81f0 100755
--- a/sfc/slicer.py
+++ b/sfc/slicer.py
@@ -222,6 +222,7 @@ if height is not None and height < 0 and z_levels[-1] > height:
 
 for i in range(0, len(z_levels)):
 	next_z = z_levels[i]
+	print >>sys.stderr, "next_z = ", next_z
 	wires = shape.slice(Base.Vector(0, 0, 1), next_z + epsilon)
 	if i == len(z_levels) - 1:
 		next_z += end