diff --git a/sk_demo/src/Mono.cs b/sk_demo/src/Mono.cs
index 0408478..f545427 100644
--- a/sk_demo/src/Mono.cs
+++ b/sk_demo/src/Mono.cs
@@ -226,9 +226,9 @@ public class Mono {
 
     Matrix palm_ori = rig.hand_1.palm.ToMatrix();
     Vec3 thumb_tip = palm_ori.Inverse * rig.hand_1.Get(FingerId.Thumb, JointId.Tip).position;
-    Vec3 index_knuckle = palm_ori.Inverse * rig.hand_1.Get(FingerId.Index, JointId.KnuckleMajor).position;
-    if (thumb_tip.z > index_knuckle.z - 1.5f * U.cm) {
-      Log.Info("thumb is up z");
+    Vec3 thumb_minor = palm_ori.Inverse * rig.hand_1.Get(FingerId.Thumb, JointId.KnuckleMinor).position;
+    if (thumb_tip.x < thumb_minor.x - 0f * U.cm) {
+      Log.Info("thumb is out");
       xi = 0;
     }