diff --git a/science-constants.cabal b/science-constants.cabal
--- a/science-constants.cabal
+++ b/science-constants.cabal
@@ -1,5 +1,5 @@
 name: science-constants
-version: 0.1.0.0
+version: 0.1.0.1
 license: OtherLicense
 license-File: LICENSE
 author: Anton Vorontsov <anton@enomsg.org>
diff --git a/src/Science/Constants/Short.hs b/src/Science/Constants/Short.hs
--- a/src/Science/Constants/Short.hs
+++ b/src/Science/Constants/Short.hs
@@ -14,3 +14,4 @@
 q_p = chargeOfProton
 q_e = chargeOfElectron
 e   = exp 1
+tau = 2*pi