diff --git a/TrimSP.html b/TrimSP.html
index 0344bce..55fa9a8 100644
--- a/TrimSP.html
+++ b/TrimSP.html
@@ -62,9 +62,10 @@
 		  <tr><td>Projectile</td>
 		    <td><select name="ProjType" id="ProjType" onchange="ProjSmartDefaults()" onload="ProjSmartDefaults()">
 			<option selected="selected" value="Muon">Muon</option>
-			<option  value="Li8">Li8</option>
-			<option  value="B12">B12</option>
-			<option  value="H">H</option>
+			<option value="Li8">Li8</option>
+			<option value="B12">B12</option>
+			<option value="Mg31">Mg31</option>
+			<option value="H">H</option>
 		      </select>
 		    </td>
 		  </tr>
diff --git a/TrimSPlib.js b/TrimSPlib.js
index 2622b61..d50114e 100644
--- a/TrimSPlib.js
+++ b/TrimSPlib.js
@@ -41,6 +41,7 @@ function Zof(Element)
 	"Muon":1,
 	"Li8":3,
 	"B12":5,
+	"Mg31":12,
 	"H":1,
 	"He":2,
 	"Li":3,
@@ -144,6 +145,7 @@ function Massof(Element)
 	"Muon":0.1134289259,
 	"Li8":8.02248624,
 	"B12":12.0143526,
+	"Mg31":30.996648,
 	"H":1.00800,
 	"He":4.00300,
 	"Li":6.93900,