diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2006-2011, Bjorn Buckwalter.
+Copyright (c) 2006-2013, Bjorn Buckwalter.
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
diff --git a/Numeric/Units/Dimensional.lhs b/Numeric/Units/Dimensional.lhs
--- a/Numeric/Units/Dimensional.lhs
+++ b/Numeric/Units/Dimensional.lhs
@@ -58,7 +58,7 @@
 > #-}
 
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
@@ -382,7 +382,7 @@
 The sum of all elements in a list.
 
 > sum :: forall d a . Num a => [Quantity d a] -> Quantity d a
-> sum = foldr (+) (Dimensional 0 :: Quantity d a)
+> sum = foldr (+) _0
 
 The length of the list as a 'Dimensionless'. This can be useful for
 purposes of e.g. calculating averages.
@@ -442,12 +442,17 @@
 > one :: Num a => Unit DOne a
 > one = Dimensional 1
 
-For convenience We define some constants for small integer values
-that often show up in formulae. We also throw in 'pi' for good
-measure.
+For convenience we define some small integer values and constants.
 
-> _0, _1, _2, _3, _4, _5, _6, _7, _8, _9 :: (Num a) => Dimensionless a
-> _0 = 0 *~ one
+The constant for zero is polymorphic as proposed by Douglas McClean
+(http://code.google.com/p/dimensional/issues/detail?id=39) allowing
+it to express zero Length or Capacitance or Velocity etc, in addition
+to the dimensionless value zero.
+
+> _0 :: (Num a) => Quantity d a
+> _0 = Dimensional 0
+
+> _1, _2, _3, _4, _5, _6, _7, _8, _9 :: (Num a) => Dimensionless a
 > _1 = 1 *~ one
 > _2 = 2 *~ one
 > _3 = 3 *~ one
@@ -458,8 +463,12 @@
 > _8 = 8 *~ one
 > _9 = 9 *~ one
 
-> pi :: (Floating a) => Dimensionless a
+For background on 'tau' see http://tauday.com/tau-manifesto (but also
+feel free to review http://www.thepimanifesto.com).
+
+> pi, tau :: (Floating a) => Dimensionless a
 > pi = Prelude.pi *~ one
+> tau = _2 * pi
 
 
 = Instances of 'Show' =
diff --git a/Numeric/Units/Dimensional/CGS.lhs b/Numeric/Units/Dimensional/CGS.lhs
--- a/Numeric/Units/Dimensional/CGS.lhs
+++ b/Numeric/Units/Dimensional/CGS.lhs
@@ -52,7 +52,7 @@
 > #-}
 > {-# OPTIONS_GHC -fcontext-stack=30 #-}
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
diff --git a/Numeric/Units/Dimensional/Extensible.lhs b/Numeric/Units/Dimensional/Extensible.lhs
--- a/Numeric/Units/Dimensional/Extensible.lhs
+++ b/Numeric/Units/Dimensional/Extensible.lhs
@@ -35,7 +35,7 @@
 > #-}
 
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
diff --git a/Numeric/Units/Dimensional/NonSI.lhs b/Numeric/Units/Dimensional/NonSI.lhs
--- a/Numeric/Units/Dimensional/NonSI.lhs
+++ b/Numeric/Units/Dimensional/NonSI.lhs
@@ -13,7 +13,7 @@
 otherwise specified.
 
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
@@ -69,12 +69,13 @@
 
 Some US customary (that is, inch-pound) units.
 
-> inch, foot :: Fractional a => Unit DLength a
+> inch, foot, mil :: Fractional a => Unit DLength a
 > inch = prefix 2.54 (centi meter)
 > foot = prefix 12 inch     -- 0.3048 m
+> mil  = prefix 0.001 inch
 > poundMass, ounce :: Fractional a => Unit DMass a
 > poundMass = prefix 0.45359237 (kilo gram)
-> ounce     = prefix 28.349523 gram
+> ounce     = prefix (1 Prelude./ 16) poundMass
 
 > poundForce :: Fractional a => Unit DForce a
 > poundForce = poundMass * gee  -- 4.4482 N
@@ -168,6 +169,21 @@
 
 > stokes :: (Fractional a) => Unit DKinematicViscosity a
 > stokes = centi meter ^ pos2 / second
+
+
+= Imperial Volumes =
+
+Per http://en.wikipedia.org/wiki/Imperial_units.
+
+> imperialGallon, imperialQuart, imperialPint, imperialCup,
+>                 imperialGill, imperialFluidOunce
+>                 :: (Fractional a) => Unit DVolume a
+> imperialGallon = prefix 4.54609 liter
+> imperialQuart  = prefix (1 Prelude./ 4) imperialGallon
+> imperialPint   = prefix (1 Prelude./ 8) imperialGallon
+> imperialCup    = prefix 0.5 imperialPint
+> imperialGill   = prefix (1 Prelude./ 4) imperialPint
+> imperialFluidOunce = prefix (1 Prelude./ 20) imperialPint
 
 
 = References =
diff --git a/Numeric/Units/Dimensional/Quantities.lhs b/Numeric/Units/Dimensional/Quantities.lhs
--- a/Numeric/Units/Dimensional/Quantities.lhs
+++ b/Numeric/Units/Dimensional/Quantities.lhs
@@ -16,7 +16,7 @@
 dimensionality type synonyms are provided for each quantity type.
 
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
diff --git a/Numeric/Units/Dimensional/SIUnits.lhs b/Numeric/Units/Dimensional/SIUnits.lhs
--- a/Numeric/Units/Dimensional/SIUnits.lhs
+++ b/Numeric/Units/Dimensional/SIUnits.lhs
@@ -11,7 +11,7 @@
 referenced are from [1] unless otherwise specified.
 
 > {- |
->    Copyright  : Copyright (C) 2006-2011 Bjorn Buckwalter
+>    Copyright  : Copyright (C) 2006-2013 Bjorn Buckwalter
 >    License    : BSD3
 >
 >    Maintainer : bjorn.buckwalter@gmail.com
@@ -262,9 +262,17 @@
 > tonne     = prefix 1000 (kilo gram) -- Name in original SI text.
 > metricTon = tonne                   -- American name.
 
+In 2012 the IAU redefined the astronomical unit as a conventional
+unit of length directly tied to the meter, with a length of exactly
+149,597,870,700 m and the official abbreviation of au[3].
 
+> astronomicalUnit :: Num a => Unit DLength a
+> astronomicalUnit = prefix 149597870700 meter
+
+
 = References =
 
 [1] http://physics.nist.gov/Pubs/SP811/
 [2] http://en.wikipedia.org/wiki/Minute_of_arc
+[3] http://en.wikipedia.org/wiki/Astronomical_unit
 
diff --git a/dimensional.cabal b/dimensional.cabal
--- a/dimensional.cabal
+++ b/dimensional.cabal
@@ -1,8 +1,8 @@
 Name:                dimensional
-Version:             0.10.2
+Version:             0.12
 License:             BSD3
 License-File:        LICENSE
-Copyright:           Bjorn Buckwalter 2006-2012
+Copyright:           Bjorn Buckwalter 2006-2013
 Author:              Bjorn Buckwalter
 Maintainer:          bjorn.buckwalter@gmail.com
 Stability:           mostly stable
