diff --git a/index.html b/index.html
index efa7018..c229fa4 100644
--- a/index.html
+++ b/index.html
@@ -384,7 +384,7 @@
 						</div>
 
 						<h3>Address Options</h3>
-						<p>You can use the advanced options below to generate different kind of master address.</p>
+						<p>You can use the advanced options below to generate different kinds of master addresses.</p>
 						
 						<div class="checkbox">
 							<label><input type="checkbox" id="newHDBrainwallet" class="checkbox-inline"> Custom Seed or Brain Wallet</label>
diff --git a/js/coin.js b/js/coin.js
index 73e108d..8f8b98b 100644
--- a/js/coin.js
+++ b/js/coin.js
@@ -439,6 +439,7 @@
 			}
 		}
 
+		// extend prv/pub key
 		r.extend = function(){
 			var hd = coinjs.hd();
 			return hd.make({'depth':(this.depth*1)+1,
@@ -449,8 +450,9 @@
 				'pubkey':this.keys.pubkey});
 		}
 
+		// derive key from index
 		r.derive = function(i){
-			i = (i)?i:0;
+			i = (i)?:0;
 			var blob = (Crypto.util.hexToBytes(this.keys.pubkey)).concat(coinjs.numToBytes(i,4).reverse());
 
 			var j = new jsSHA(Crypto.util.bytesToHex(blob), 'HEX');
@@ -469,6 +471,7 @@
 			o.child_index = i;
 
 			if(this.type=='private'){
+				// derive xpub/xprv from a xprv key
 				k = il.add(new BigInteger([0].concat(Crypto.util.hexToBytes(this.keys.privkey)))).mod(ecparams.getN());
 				key = Crypto.util.bytesToHex(k.toByteArrayUnsigned());
 
@@ -480,6 +483,7 @@
 					'address':coinjs.pubkey2address(pubkey)};
 
 			} else if (this.type=='public'){
+				// derive xpub key from an xpub key
 				q = ecparams.curve.decodePointHex(this.keys.pubkey);
 				var curvePt = ecparams.getG().multiply(il).add(q);
 
@@ -535,12 +539,12 @@
 			//child index
 			k = k.concat((coinjs.numToBytes(data.child_index, 4)).reverse());
 
-			// Chain code
+			//Chain code
 			k = k.concat(data.chain_code);
 
 			var o = {}; // results
 
-			// Extended HD Private Key
+			//encode xprv key
 			if(data.privkey){
 				var prv = (coinjs.numToBytes(coinjs.hdkey.prv, 4)).reverse();
 				prv = prv.concat(k);
@@ -552,7 +556,7 @@
 				o.privkey = coinjs.base58encode(ret);
 			}
 
-			// Extended HD Public Key
+			//encode xpub key
 			if(data.pubkey){
 				var pub = (coinjs.numToBytes(coinjs.hdkey.pub, 4)).reverse();
 				pub = pub.concat(k);
diff --git a/sha1sum b/sha1sum
index 632e068..01cfe05 100644
--- a/sha1sum
+++ b/sha1sum
@@ -10,7 +10,7 @@ f7c09f2f5a721371e7d478050119f7e2d58e3ef9  ./js/crypto-sha256-hmac.js
 ad038e1f39646b68ae666324ed4c2882a8c42474  ./js/qrcode.js
 64eb4ea5c882f8bce3e1885bf00728455f1c2f4c  ./js/ripemd160.js
 114089ef2a3feb6d4db4f9cabcb186d7750d5884  ./js/sha512.js
-b7d72e6064cf8a1a0b5a602bc2a976ce3d61aadf  ./js/coin.js
+6db735d6bc9fbacd7a874ad3c4dee92b6f8d95ce  ./js/coin.js
 8e921b2156d232871540e168e1677368b5611dc9  ./js/coinbin.js
 ae49e56999d82802727455f0ba83b63acd90a22b  ./js/jquery-1.9.1.min.js
 5f570018ed044eafd464f7e0ab1783b966224055  ./LICENCE
@@ -25,4 +25,4 @@ de51a8494180a6db074af2dee2383f0a363c5b08  ./fonts/glyphicons-halflings-regular.s
 278e49a86e634da6f2a02f3b47dd9d2a8f26210f  ./fonts/glyphicons-halflings-regular.woff
 44bc1850f570972267b169ae18f1cb06b611ffa2  ./fonts/glyphicons-halflings-regular.ttf
 fe8d57914bb036ab94e86ec35b2671eeb6d20d0d  ./README.md
-44ab99a496aab01d8181e0f2ac9b02ad8b854d9d  ./index.html
+954c6edeac5881c4e12b3db46875a6eab18239b8  ./index.html