diff --git a/aviation-weight-balance.cabal b/aviation-weight-balance.cabal
--- a/aviation-weight-balance.cabal
+++ b/aviation-weight-balance.cabal
@@ -1,5 +1,5 @@
 name:               aviation-weight-balance
-version:            0.0.2
+version:            0.0.3
 license:            BSD3
 license-file:       LICENCE
 author:             Tony Morris <ʇǝu˙sıɹɹoɯʇ@ןןǝʞsɐɥ>, Joshua Morris <ɯoɔ˙lᴉɐɯƃ@llǝʞsɐɥ+sᴉɹɹoɯuɥoɾɐnɥsoɾ>
@@ -27,7 +27,7 @@
   build-depends:
                     base >= 4.8 && < 5
                     , lens >= 4.15 && < 5
-                    , aviation-units >= 0.0.2 && < 1
+                    , aviation-units >= 0.0.3 && < 1
 
   if impl(ghc < 8)
     build-depends:
diff --git a/changelog b/changelog
--- a/changelog
+++ b/changelog
@@ -1,3 +1,7 @@
+0.0.3
+
+* Add millimetres
+
 0.0.2
 
 * Update GHC
diff --git a/src/Data/Aviation/WB/Arm/ArmRangeLower.hs b/src/Data/Aviation/WB/Arm/ArmRangeLower.hs
--- a/src/Data/Aviation/WB/Arm/ArmRangeLower.hs
+++ b/src/Data/Aviation/WB/Arm/ArmRangeLower.hs
@@ -11,7 +11,7 @@
 
 import Control.Category((.))
 import Control.Lens(Lens', Traversal', Setter', makeClassy, iso)
-import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Thouinches(thouinches))
+import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Millimetres(millimetres), Thouinches(thouinches))
 import Data.Eq(Eq)
 import Data.Maybe(Maybe)
 import Data.Monoid(Monoid(mempty, mappend))
@@ -67,6 +67,10 @@
 instance Centimetres ArmRangeLower where
   centimetres =
     dividing (254 % 100) . inches
+
+instance Millimetres ArmRangeLower where
+  millimetres =
+    dividing (254 % 10) . inches
 
 instance Semigroup ArmRangeLower where
   (<>) =
diff --git a/src/Data/Aviation/WB/Arm/ArmRangeUpper.hs b/src/Data/Aviation/WB/Arm/ArmRangeUpper.hs
--- a/src/Data/Aviation/WB/Arm/ArmRangeUpper.hs
+++ b/src/Data/Aviation/WB/Arm/ArmRangeUpper.hs
@@ -11,7 +11,7 @@
 
 import Control.Category((.))
 import Control.Lens(Lens', Traversal', Setter', makeClassy, iso)
-import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Thouinches(thouinches))
+import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Millimetres(millimetres), Thouinches(thouinches))
 import Data.Eq(Eq)
 import Data.Maybe(Maybe)
 import Data.Monoid(Monoid(mempty, mappend))
@@ -67,7 +67,11 @@
 instance Centimetres ArmRangeUpper where
   centimetres =
     dividing (254 % 100) . inches
-    
+
+instance Millimetres ArmRangeUpper where
+  millimetres =
+    dividing (254 % 10) . inches
+
 instance Semigroup ArmRangeUpper where
   (<>) =
     mappend
diff --git a/src/Data/Aviation/WB/Arm/ArmStatic.hs b/src/Data/Aviation/WB/Arm/ArmStatic.hs
--- a/src/Data/Aviation/WB/Arm/ArmStatic.hs
+++ b/src/Data/Aviation/WB/Arm/ArmStatic.hs
@@ -11,7 +11,7 @@
 
 import Control.Category((.))
 import Control.Lens(Lens', Traversal', Setter', makeClassy, iso)
-import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Thouinches(thouinches))
+import Data.Aviation.Units(Inches(inches), Centimetres(centimetres), Millimetres(millimetres), Thouinches(thouinches))
 import Data.Eq(Eq)
 import Data.Maybe(Maybe)
 import Data.Monoid(Monoid(mempty, mappend))
@@ -67,6 +67,10 @@
 instance Centimetres ArmStatic where
   centimetres =
     dividing (254 % 100) . inches
+
+instance Millimetres ArmStatic where
+  millimetres =
+    dividing (254 % 10) . inches
 
 instance Semigroup ArmStatic where
   (<>) =