Add Hammer units

macrovision.js

@@ -254,6 +254,13 @@ math.createUnit("donkeySeconds", {
     definition: "250 joules",
     prefixes: "long"
 })
+math.createUnit("HU", {
+    definition: "0.75 inches",
+    aliases: [
+        "HUs",
+        "hammerUnits"
+    ]
+});
 
 const defaultUnits = {
     length: {
@@ -321,7 +328,8 @@ const unitChoices = {
             "beardSeconds",
             "points",
             "smoots",
-            "furlongs"
+            "furlongs",
+            "HUs"
         ]
     },
     area: {