diff --git a/prototype/circles.py b/prototype/circles.py
index f4cbffb..322b670 100644
--- a/prototype/circles.py
+++ b/prototype/circles.py
@@ -64,30 +64,32 @@ def svg_puzzle(p, size, angle):
     return text
 
 def svg_line_puzzle(start, end, puzzle_scale=1.0, linewidth=0.50):
-    v = end - start
-    dist = np.linalg.norm(v)
-    size = dist / 10.0 * puzzle_scale
-    v = v / dist
-    angle = math.atan2(v[1], v[0])
-
-    p = np.mean([start, end], axis=0)
-
+    # draws a line from start to end with a simple jigsaw puzzle style cutout in the middle
+    # the size of the cutout can be controlled with the puzzle_scale parameter
     # compute points
     """
         v1 and v2 are orthogonal vectors
 
-        construction of points (starting at p):
+        construction of points (starting at p (middle between start and end)):
 
-           p3 <------   -2 v1  ------ p2
-                                      ^
-                                      |
-                                      v2
-                                      |
-                                      |
-           p4 <-- -v1 --  p -- v1 --> p1
+                 p2 -------   2 v1  -----> p3
+                  ^
+                  |
+                 v2
+                  |
+                  |
+     start ---   p1 <-- -v1 --  p -- v1 --> p4   --- end
 
         then between points p2 and p3 with draw an arc
     """
+    v = end - start
+    dist = np.linalg.norm(v)
+    size = dist / 10.0 * puzzle_scale   # size of the cutout
+    v = v / dist
+    angle = math.atan2(v[1], v[0])  # angle of v
+
+    # midpoint between start and end
+    p = np.mean([start, end], axis=0)
 
     v1 = np.array([np.cos(angle), np.sin(angle)])
     v2 = np.array([v1[1], -v1[0]])