diff --git a/lib/OpenLayers/Util.js b/lib/OpenLayers/Util.js
index 121d99f769..25f11e2106 100644
--- a/lib/OpenLayers/Util.js
+++ b/lib/OpenLayers/Util.js
@@ -879,6 +879,7 @@ OpenLayers.Util.createUniqueID = function(prefix) {
 /**
  * Constant: INCHES_PER_UNIT
  * {Object} Constant inches per unit -- borrowed from MapServer mapscale.c
+ * derivation of nautical miles from http://en.wikipedia.org/wiki/Nautical_mile
  */
 OpenLayers.INCHES_PER_UNIT = { 
     'inches': 1.0,
@@ -886,10 +887,12 @@ OpenLayers.INCHES_PER_UNIT = {
     'mi': 63360.0,
     'm': 39.3701,
     'km': 39370.1,
-    'dd': 4374754
+    'dd': 4374754,
+    'yd': 36
 };
 OpenLayers.INCHES_PER_UNIT["in"]= OpenLayers.INCHES_PER_UNIT.inches;
 OpenLayers.INCHES_PER_UNIT["degrees"] = OpenLayers.INCHES_PER_UNIT.dd;
+OpenLayers.INCHES_PER_UNIT["nmi"] = 1852 * OpenLayers.INCHES_PER_UNIT.m;		
 
 /** 
  * Constant: DOTS_PER_INCH