diff --git a/phone.scad b/phone.scad
index f65cae5..8b37314 100644
--- a/phone.scad
+++ b/phone.scad
@@ -4,6 +4,8 @@ use <primitives.scad>
 
 $fs = 1;
 
+// tolerance. lining up the extrusions and cuts with zero tolerance causes very thin walls,
+// so i offset those to make the model actually contiguous.
 Tol = 0.1;
 
 // simple box-shaped body; preserve for easier debugging