diff --git a/pbrt/01/index.html b/pbrt/01/index.html
index 69005d0..35fb8f5 100644
--- a/pbrt/01/index.html
+++ b/pbrt/01/index.html
@@ -98,6 +98,11 @@
         return sum;
     }
 
+    function normal_dist(mean, variance, x) {
+        const dx = x - mean;
+        return (1 / Math.sqrt(2 * Math.PI * variance)) * Math.exp(-(dx * dx) / (2 * variance));
+    }
+
     function monte_carlo(from, to, func, iter) {
         let sum = 0;
         for (let i = 0; i < iter; i += 1) {
@@ -109,12 +114,19 @@
 
     function integrate(from, to, func) {
         const max_iter = 16384;
-        table_element.innerHTML = '<tr><th>N</th><th>Monte Carlo</th><th>Trapezoid</th></tr>';
+        const m = [];
+        const t = [];
+        table_element.innerHTML = '<tr><th>N</th><th>Monte Carlo</th><th>MSE</th><th>Trapezoid</th></tr>';
         
         for (let i = 1; i <= max_iter; i *= 2) {
-            const m = monte_carlo(from, to, func, i);
-            const t = trapezoid(from, to, func, i);
-            table_element.innerHTML += '<tr><th>' + i + '</th><th>' + m.toFixed(3) + '</th><th>' + t.toFixed(3) + '</th></th>';
+            m.push(monte_carlo(from, to, func, i));
+            t.push(trapezoid(from, to, func, i));
+        }
+
+        const E = t[m.length - 1];            
+        for (let i = 0; i < m.length; i += 1) {
+            const mse = (m[i] - E) * (m[i] - E);
+            table_element.innerHTML += '<tr><th>' + Math.pow(2, i) + '</th><th>' + m[i].toFixed(3) + '</th><th>' + mse.toFixed(3) + '</th><th>' + t[i].toFixed(3) + '</th></th>';
         }
     }
 
@@ -146,7 +158,12 @@
         }
     }
 
-    const initial_expr = 'cos(x) + sin(2x) + 2cos(4x^2)';
+    for (let i = 0; i <= 10; i += 1) {
+        const t = i / 10 * 2 - 1;
+        console.log(t + ': ' + normal_dist(0, 0.2, t));
+    }
+
+    const initial_expr = 'sqrt(x)+2x-3x^2+x^3sin(x)';
     expr_element.value = initial_expr;
     from_element.valueAsNumber = 0;
     to_element.valueAsNumber = 3;