diff --git a/README.md b/README.md
index 171df70..959dc53 100644
--- a/README.md
+++ b/README.md
@@ -2,3 +2,10 @@ measure-stick
 =============
 
 A simple bookmarklet for measuring pixels on a webpage
+
+Save as a bookmark in your browser. Click the bookmarklet to add the
+measure-stick to the page.
+
+The orange square can be moved with the arrow keys, or be dragged
+around. Resize by holding alt and using the arrow keys. Press shift to
+move or resize in steps of 10 pixels.
diff --git a/bookmarklet.js b/bookmarklet.js
new file mode 100644
index 0000000..24cf007
--- /dev/null
+++ b/bookmarklet.js
@@ -0,0 +1,55 @@
+javascript:(function($) {
+
+	var jqui = $.getScript('//code.jquery.com/ui/1.10.3/jquery-ui.js', function() {
+		var ms = $('<div></div>');
+		ms.css({
+			backgroundColor: 'orange',
+			height: '10px',
+			left: '20px',
+			position: 'absolute',
+			top: '20px',
+			width: '10px',
+			zIndex: '999999'
+		}).appendTo('body').draggable({ grid: [ 20, 20 ] });
+
+		$(document).keydown(function(e) {
+			var step = e.shiftKey ? 10 : 1;
+
+			switch (e.keyCode) {
+			case 37: /* left */
+				if (e.altKey) {
+					ms.width(ms.width() - step);
+				} else {
+					ms.css('left', (parseInt(ms.offset().left, 10) - step) + 'px');
+				}
+				break;
+			case 38: /* up */
+				if (e.altKey) {
+					ms.height(ms.height() - step);
+				} else {
+					ms.css('top', (parseInt(ms.offset().top, 10) - step) + 'px');
+				}
+				break;
+			case 39: /* right */
+				if (e.altKey) {
+					ms.width(ms.width() + step);
+				} else {
+					ms.css('left', (parseInt(ms.offset().left, 10) + step) + 'px');
+				}
+				break;
+			case 40: /* down */
+				if (e.altKey) {
+					ms.height(ms.height() + step);
+				} else {
+					ms.css('top', (parseInt(ms.offset().top, 10) + step) + 'px');
+				}
+				break;
+			default:
+				return true;
+			}
+
+			return false;
+		});
+	});
+
+}(jQuery))
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