diff --git a/index.html b/index.html
index 887c04b..62d3878 100644
--- a/index.html
+++ b/index.html
@@ -157,6 +157,8 @@
         fill('white');
         translate(30, 200, 0);
         Textline.restart();
+        Textline.put('heading');
+        Textline.put(heading);
         Textline.put('ang');
         Textline.put(target.ang);
         Textline.put('angerr');
diff --git a/js/classes.js b/js/classes.js
index ee7aca2..acd18ce 100644
--- a/js/classes.js
+++ b/js/classes.js
@@ -26,7 +26,7 @@ class Sounder {
     //
     // this.ang = getBearing(latitude, longitude, this.latitude, this.longitude);  (deg)
     this.ang = getBearing(latitude, longitude, this.latitude, this.longitude); // (deg)
-    this.angerr = (((this.ang - heading + 360) % 360) + 180) % 360 - 180;
+    this.angerr = (heading - this.ang + 360) % 360;
     this.dist = getDistance(latitude, longitude, this.latitude, this.longitude); // (km)
     //
     this.distvol = map(this.dist, this.distmap[0], this.distmap[1], this.distmap[2], this.distmap[3], true); //(dB)
@@ -106,7 +106,7 @@ class Compass {
     circle(0, 0, 0.9);
     //
     fill(this.colors[1]);
-    rotate(this.heading);
+    rotate(this.heading * -1);
     quad(0.1, 0.2, 0, -0.4, -0.1, 0.2, 0, 0.1);
     //
     fill(this.colors[2]);
diff --git a/js/util.js b/js/util.js
index d1c121b..87f585d 100644
--- a/js/util.js
+++ b/js/util.js
@@ -8,7 +8,7 @@ if (navigator.userAgent.match(/(iPod|iPhone|iPad)/)) {
         if (response == 'granted') {
           window.addEventListener("deviceorientation", (event) => {
             if (event.webkitCompassHeading) {
-              heading = event.webkitCompassHeading;
+              heading = (event.webkitCompassHeading + 180) % 360 - 180; // EAST == +90, WEST == -90
             }
           }, true);
         }
@@ -17,7 +17,7 @@ if (navigator.userAgent.match(/(iPod|iPhone|iPad)/)) {
   }
 } else {
   window.addEventListener("deviceorientationabsolute", (event) => {
-    heading = event.alpha * -1;
+    heading = ((360 - event.alpha) + 180) % 360 - 180; // EAST == +90, WEST == -90
   }, true);
 }