diff -r ff62016e051d -r 9ee8c00ae5b7 src/widgets/Sparkline.js
--- a/src/widgets/Sparkline.js	Tue Nov 06 10:59:57 2012 +0100
+++ b/src/widgets/Sparkline.js	Fri Nov 09 14:33:03 2012 +0100
@@ -20,11 +20,20 @@
         _list = this.getWidgetAnnotations();
     
     for (var _i = 0; _i < this.slice_count; _i++) {
-        var _begin = new IriSP.Model.Time(_i*_duration/this.slice_count),
-            _end = new IriSP.Model.Time((_i+1)*_duration/this.slice_count),
-            _annotations = _list.filter(function(_annotation) {
-                return _annotation.begin >= _begin && _annotation.end < _end;
-            }).length;
+        var _begin = (_i*_duration/this.slice_count),
+            _end = ((_i+1)*_duration/this.slice_count),
+            _annotations = _list.reduce(function(_m, _annotation) {
+                if (_annotation.begin < _end && _annotation.begin >= _begin) {
+                    var _d = _annotation.getDuration().milliseconds;
+                    if (!_d) {
+                        return _m + 1;
+                    } else {
+                        return _m + (Math.min(_annotation.end, _end) - Math.max(_annotation.begin, _begin)) / _d;
+                    }
+                } else {
+                    return _m
+                }
+            },0);
         _max = Math.max(_max, _annotations);
         _slices.push(_annotations);
     }