diff --git a/Makefile.am b/Makefile.am
index 56c508b..743a7b3 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -46,7 +46,7 @@ BUILT_SOURCES = frontends/LexOccam.hs frontends/LexRain.hs CompilerCommands.hs
 CLEANFILES = $(BUILT_SOURCES)
 
 tock_SOURCES = transformations/SimplifyExprs.hs transformations/SimplifyTypes.hs 
-tock_SOURCES += transformations/Unnest.hs transformations/UsageCheck.hs transformations/SimplifyProcs.hs
+tock_SOURCES += transformations/Unnest.hs transformations/RainUsageCheck.hs transformations/SimplifyProcs.hs
 tock_SOURCES += transformations/SimplifyComms.hs
 tock_SOURCES += frontends/PreprocessOccam.hs frontends/ParseRain.hs frontends/StructureOccam.hs
 tock_SOURCES += frontends/ParseOccam.hs frontends/RainTypes.hs frontends/RainPasses.hs frontends/ParseUtils.hs
@@ -60,7 +60,7 @@ tock_SOURCES += backends/GenerateC.hs backends/GenerateCPPCSP.hs
 tock_SOURCES += Main.hs
 
 tocktest_SOURCES = $(tock_SOURCES)
-tocktest_SOURCES += transformations/PassTest.hs transformations/UsageCheckTest.hs
+tocktest_SOURCES += transformations/PassTest.hs transformations/RainUsageCheckTest.hs
 tocktest_SOURCES += backends/GenerateCTest.hs backends/BackendPassesTest.hs
 tocktest_SOURCES += common/TestUtil.hs common/CommonTest.hs common/FlowGraphTest.hs
 tocktest_SOURCES += frontends/ParseRainTest.hs frontends/RainPassesTest.hs frontends/RainTypesTest.hs
diff --git a/TestMain.hs b/TestMain.hs
index 87440fe..6d4988c 100644
--- a/TestMain.hs
+++ b/TestMain.hs
@@ -32,7 +32,7 @@ with this program.  If not, see <http://www.gnu.org/licenses/>.
 --
 -- * "RainPassTest"
 --
--- * "UsageCheckTest"
+-- * "RainUsageCheckTest"
 module TestMain () where
 
 import Test.HUnit
@@ -45,7 +45,7 @@ import qualified ParseRainTest (tests)
 import qualified PassTest (tests)
 import qualified RainPassesTest (tests)
 import qualified RainTypesTest (tests)
-import qualified UsageCheckTest (tests)
+import qualified RainUsageCheckTest (tests)
 
 main :: IO ()
 main = do runTestTT $ TestList
@@ -58,6 +58,6 @@ main = do runTestTT $ TestList
               ,PassTest.tests
               ,RainPassesTest.tests
               ,RainTypesTest.tests
-              ,UsageCheckTest.tests
+              ,RainUsageCheckTest.tests
             ]
           return ()
diff --git a/transformations/UsageCheck.hs b/transformations/RainUsageCheck.hs
similarity index 95%
rename from transformations/UsageCheck.hs
rename to transformations/RainUsageCheck.hs
index 5598cce..dfc1be8 100644
--- a/transformations/UsageCheck.hs
+++ b/transformations/RainUsageCheck.hs
@@ -16,7 +16,11 @@ You should have received a copy of the GNU General Public License along
 with this program.  If not, see <http://www.gnu.org/licenses/>.
 -}
 
-module UsageCheck where
+-- | This code implements the usage checking in Rain.  It is designed to work with
+-- the control-flow graph stuff, hence the use of functions that match the dictionary
+-- of functions in FlowGraph.  This is also why we don't drill down into processes;
+-- the control-flow graph means that we only need to concentrate on each node that isn't nested.
+module RainUsageCheck where
 
 import Data.Generics
 import Data.List
diff --git a/transformations/UsageCheckTest.hs b/transformations/RainUsageCheckTest.hs
similarity index 99%
rename from transformations/UsageCheckTest.hs
rename to transformations/RainUsageCheckTest.hs
index 727e6e5..0fb345f 100644
--- a/transformations/UsageCheckTest.hs
+++ b/transformations/RainUsageCheckTest.hs
@@ -16,7 +16,7 @@ You should have received a copy of the GNU General Public License along
 with this program.  If not, see <http://www.gnu.org/licenses/>.
 -}
 
-module UsageCheckTest (tests) where
+module RainUsageCheckTest (tests) where
 
 import Prelude hiding (fail)
 import Test.HUnit
@@ -24,7 +24,7 @@ import Test.HUnit
 
 import qualified AST as A
 import TestUtil
-import qualified UsageCheck as UC
+import RainUsageCheck
 
 
 --See note in UsageCheck about WrittenRead not using sets.  Therefore our equality function is inefficient