diff --git a/MatlabCodes/Chapter 02/Fig02_06.m b/MatlabCodes/Chapter 02/Fig02_06.m
index a2029fa..d022a62 100644
--- a/MatlabCodes/Chapter 02/Fig02_06.m	
+++ b/MatlabCodes/Chapter 02/Fig02_06.m	
@@ -27,7 +27,7 @@
 
 s = 0;
 for i=1:length(X)-1
-    s = (X(i+1)-X(i)-mu*dt)^2;
+    s = s + (X(i+1)-X(i)-mu*dt)^2;
 end
 sigma = sqrt(s/(m*dt))