diff --git a/analysis/analyse.js b/analysis/analyse.js
index 08f8ca3..b0a2704 100644
--- a/analysis/analyse.js
+++ b/analysis/analyse.js
@@ -1,3 +1,40 @@
+// http://codereview.stackexchange.com/questions/37028/grouping-elements-in-array-by-multiple-properties
+function groupBy(array, f)
+{
+    var groups = {};
+    array.forEach(function(o) {
+        var group = JSON.stringify(f(o));
+        groups[group] = groups[group] || [];
+        groups[group].push(o);
+    });
+
+    return Object.keys(groups).map(function(group) {
+        return groups[group];
+    })
+}
+
+function compareRecommendationStyle(style1, style2) {
+
+    if (style1.recommendation_style[4] === 'B' && style2.recommendation_style[4] !== 'B') {
+        return -1;
+    }
+
+    if (style2.recommendation_style[4] === 'B' && style1.recommendation_style[4] !== 'B') {
+        return 1;
+    }
+
+    if (style1.recommendation_style[4] === 'V' && style2.recommendation_style[4] === 'A') {
+        return -1;
+    }
+
+    if (style2.recommendation_style[4] === 'V' && style1.recommendation_style[4] === 'A') {
+        return 1;
+    }
+
+    return 0;
+
+}
+
 function main(path) {
 
     var db = JSON.parse(require('fs').readFileSync(path, 'utf8'));
@@ -8,45 +45,152 @@ function main(path) {
     var meanTimeArrow = 0;
     var meanTimeViewport = 0;
 
-    console.log();
+    var groups = makeGroups(db);
 
-    for (var i = 0; i < db.experiments.length; i++) {
+    groups.forEach(function(elt) {
+        var ok = true;
 
-        var exp = db.experiments[i];
-        var events = exp.elements.events;
-
-        if (events.length === 0 || exp.user.worker_id === null) {
-
-            continue;
-
-        }
-
-        var coins = [];
-        for (var j = 0; j < exp.elements.events.length; j++) {
-
-            if (exp.elements.events[j].type === 'coin') {
-
-                if (coins.find(function(elt) { return elt.id === exp.elements.events[j].id; }) === undefined) {
-
-                    coins.push(exp.elements.events[j]);
-
-                }
+        // console.log(elt);
+        elt.sort(compareRecommendationStyle);
+        // console.log(elt);
 
+        elt.forEach(function(subElt) {
+            if (subElt.coin_combination_id !== elt[0].coin_combination_id) {
+                ok = false;
             }
+        });
 
+        if (!ok) {
+            process.stderr.write('Error : assertion failed');
+            process.exit(-1);
+        }
+
+        console.log(elt.length + ' -> ' + elt[0].coin_combination_id);
+    });
+
+    console.log('-----------------');
+
+    var value = minDifferences(groups);
+    console.log(value);
+
+    // for (var i = 0; i < db.experiments.length; i++) {
+
+    //     var exp = db.experiments[i];
+    //     var events = exp.elements.events;
+
+    //     if (events.length === 0 || exp.user.worker_id === null) {
+
+    //         continue;
+
+    //     }
+
+    //     var coins = [];
+    //     for (var j = 0; j < exp.elements.events.length; j++) {
+
+    //         if (exp.elements.events[j].type === 'coin') {
+
+    //             if (coins.find(function(elt) { return elt.id === exp.elements.events[j].id; }) === undefined) {
+
+    //                 coins.push(exp.elements.events[j]);
+
+    //             }
+
+    //         }
+
+    //     }
+    //     console.log(`${exp.id} -> ${coins.length} (on ${exp.coinCombination.scene_id} )`);
+    // }
+
+    // console.log();
+
+    // for (var i = 0; i < db.users.length; i++) {
+
+    //     var user = db.users[i];
+    //     console.log(`${user.worker_id} has done ${user.experiments.length} experiments with rating ${user.rating}`);
+
+    // }
+
+}
+
+function minDifference(exps) {
+
+    var dict = {};
+
+    exps.forEach(function(subElt) {
+        dict[subElt.recommendation_style[4]] = subElt.duration;
+    });
+
+    if (dict.B !== undefined) {
+
+        if (dict.A !== undefined && dict.V !== undefined) {
+            return (
+                Math.min(dict.A - dict.B, dict.V - dict.B)
+            );
+        }
+
+        if (dict.A !== undefined) {
+            return dict.A - dict.B;
+        }
+
+        if (dict.V !== undefined) {
+            return dict.V - dict.B;
         }
-        console.log(`${exp.id} -> ${coins.length} (on ${exp.coinCombination.scene_id} )`);
     }
 
-    console.log();
+}
 
-    for (var i = 0; i < db.users.length; i++) {
+function minDifferences(groups) {
 
-        var user = db.users[i];
-        console.log(`${user.worker_id} has done ${user.experiments.length} experiments with rating ${user.rating}`);
+    var differences = [];
 
+    groups.forEach(function(elt) {
+
+        var timesMean = 0;
+
+        elt.forEach(function(elt) {
+            var duration = experimentDuration(elt);
+            timesMean += experimentDuration(elt);
+        });
+
+        timesMean /= elt.length;
+
+        var normalizedElt = [];
+
+        elt.forEach(function(subElt) {
+            normalizedElt.push({
+                recommendation_style : subElt.recommendation_style,
+                duration : experimentDuration(subElt) / timesMean
+            });
+        });
+
+        var diff = minDifference(normalizedElt);
+
+        if (diff !== undefined)
+            differences.push(diff);
+    });
+
+    var sum = 0;
+
+    differences.forEach(function(elt) {
+        sum += elt;
+    });
+
+    return sum / differences.length;
+
+}
+
+function experimentDuration(exp) {
+    var lastCoin = null;
+
+    for (var i = exp.elements.events.length - 1; i >= 0; i--) {
+        if (exp.elements.events[i].type === 'coin') {
+            lastCoin = exp.elements.events[i];
+            break;
+        }
     }
 
+    return timeDifference(exp.elements.events[0].time, lastCoin.time);
+
 }
 
 function timeDifference(time1, time2) {
@@ -63,6 +207,26 @@ function timeToString(_time) {
 
 }
 
+function makeGroups(db) {
+
+    var elements = [];
+
+    for (var i = 0; i < db.experiments.length; i++) {
+
+        if (db.experiments[i].coinCombination.scene_id !== 1 && db.experiments[i].elements.events.length !== 0) {
+
+            elements.push(db.experiments[i]);
+
+        }
+
+    }
+
+    return groupBy(elements, function(item) {
+        return item.coin_combination_id;//, item.user.rating];
+    });
+
+}
+
 if (process.argv.length !== 3) {
     process.stderr.write('Error : please give me a JSON file to work on\n');
     process.exit(-1);
diff --git a/controllers/intro/views/index.jade b/controllers/intro/views/index.jade
index e8d45a2..d54928f 100644
--- a/controllers/intro/views/index.jade
+++ b/controllers/intro/views/index.jade
@@ -12,7 +12,8 @@ block content
 
 block extrajs
     script.
-        if ($.browser.chrome || $.browser.mozilla) {
+        var isOpera = window.navigator.userAgent.indexOf("OPR") > -1 || window.navigator.userAgent.indexOf("Opera") > -1;
+        if (($.browser.chrome || $.browser.mozilla) && !isOpera) {
             $('#start').html('You can now <a href="/user-study">start when you are ready</a>');
         } else {
             $('#start').html('Sorry, your browser is not compatible... please try again with Firefox or Chrome');
diff --git a/controllers/prototype/views/prototype.jade b/controllers/prototype/views/prototype.jade
index 305182f..35b9618 100644
--- a/controllers/prototype/views/prototype.jade
+++ b/controllers/prototype/views/prototype.jade
@@ -37,8 +37,8 @@ block content
                 //-input#fullarrow(type="checkbox", style={'margin-right': '10px', 'margin-bottom': '10px'})
                 //-label(for="fullarrow" style={'margin-right':'10px'}) Full arrow
 
-                input#lock(type="checkbox", style={'margin-right': '10px', 'margin-bottom': '10px'}, checked)
-                label(for="lock" style={'margin-right':'10px'}) Pointer lock
+                input#lock(type="checkbox", style={'zoom':'1.7'}, checked)
+                label(for="lock" style={'margin-right':'10px', 'zoom': '1.7'}) Pointer lock
 
                 input#showarrows(type="checkbox", style={'margin-right': '10px', 'margin-bottom': '10px', 'display':'none'}, checked)
                 label(for="showarrows" style={'margin-right':'10px', 'display': 'none'}) Show arrows
diff --git a/js/l3d/apps/prototype/tutorial/TutorialSteps.js b/js/l3d/apps/prototype/tutorial/TutorialSteps.js
index d4cc4f6..3668a96 100644
--- a/js/l3d/apps/prototype/tutorial/TutorialSteps.js
+++ b/js/l3d/apps/prototype/tutorial/TutorialSteps.js
@@ -258,7 +258,7 @@ TutorialSteps.prototype.alert = function(myString, justclicked) {
 
 TutorialSteps.prototype.notify = function(myString, justclick) {
     $('#alert-placeholder').html(
-        '<div id="toto" class="alert alert-warning alert-dismissable">' +
+        '<div id="toto" class="alert alert-info alert-dismissable">' +
             (justclick ?
             '<button type="button" class="close" aria-hidden="true"' +
                      'onclick="setTimeout(onWindowResize, 100); nextStep();' + '">' +
@@ -275,6 +275,12 @@ TutorialSteps.prototype.notify = function(myString, justclick) {
     $('#toto').removeClass('alert-info').addClass('alert-danger');
 
     setTimeout(function() {
-        $('#toto').removeClass('alert-danger').addClass('alert-warning');
-    }, 500);
+        $('#toto').removeClass('alert-danger').addClass('alert-info');
+        setTimeout(function() {
+            $('#toto').removeClass('alert-info').addClass('alert-danger');
+            setTimeout(function() {
+                $('#toto').removeClass('alert-danger').addClass('alert-info');
+            }, 700);
+        }, 700);
+    }, 700);
 };