diff --git a/testApp/test.db b/testApp/test.db
index ad4ac5b..86c4f91 100644
--- a/testApp/test.db
+++ b/testApp/test.db
@@ -30,3 +30,19 @@ record(longin, "$(P)async:cnt") {
   field(INP , "@test4")
   field(SCAN, "1 second")
 }
+
+
+record(ao, "$(P):A-SP") {
+  field(DTYP, "Raw Python Device")
+  field(OUT , "@test5 hello none")
+}
+
+record(ao, "$(P):B-SP") {
+  field(DTYP, "Raw Python Device")
+  field(OUT , "@test5 hello half")
+}
+
+record(ai, "$(P):A-RB") {
+  field(DTYP, "Raw Python Device")
+  field(INP , "@test5 hello none")
+}
diff --git a/testApp/test4.py b/testApp/test4.py
index f3a56a7..7287eec 100644
--- a/testApp/test4.py
+++ b/testApp/test4.py
@@ -14,7 +14,7 @@ class Counter(object):
     def process(self, rec, reason):
         if reason is AsyncComplete:
             rec.VAL = self.nextval
-            
+
         else:
             self.nextval = rec.VAL+1
             self.timer = threading.Timer(0.2, rec.asyncFinish, kwargs={'reason':AsyncComplete})
diff --git a/testApp/test5.py b/testApp/test5.py
new file mode 100644
index 0000000..cc0ede6
--- /dev/null
+++ b/testApp/test5.py
@@ -0,0 +1,70 @@
+
+import threading
+from devsup.hooks import addHook
+from devsup.util import Worker
+from devsup.db import IOScanListThread
+
+#(forwardfn, reversefn)
+_fns = {
+    'none':(lambda x:x, lambda x:x),
+    'half':(lambda x:x*2.0, lambda x:x/2.0),
+}
+
+ReSync = object()
+
+instances = {}
+
+class UnitWorker(object):
+    def __init__(self, name):
+        super(UnitWorker,self).__init__()
+        self.name = name
+        self.scan = IOScanListThread()
+        self.scan.force = 0
+
+        self.worker = Worker()
+
+        addHook('AfterIocRunning', self.worker.start)
+        addHook('AtIocExit', self.worker.join)
+
+    def add(self, rec, unit, val):
+        self.worker.add(self.update, (rec, unit, val))
+
+    def update(self, rec, unit, val):
+        F, _ = _fns[unit]
+        V = F(val)
+
+        values = {}
+
+        for U,(F,R) in _fns.iteritems():
+            values[U] = R(V)
+
+        self.scan.interrupt(reason=values)
+
+class UnitSupport(object):
+    def __init__(self, rec, args):
+        worker, self.unit = args.split(None, 1)
+        try:
+            W = instances[worker]
+        except KeyError:
+            W = UnitWorker(worker)
+            instances[worker] = W
+
+        self.worker = W
+        W.scan.add(rec)
+
+    def detach(self, rec):
+        self.worker.scan.remove(rec)
+
+    def process(self, rec, reason):
+        if reason is None:
+            self.worker.update(rec, self.unit, rec.VAL)
+
+        else:
+            try:
+                rec.VAL = reason[self.unit]
+                rec.UDF = 0
+            except:
+                rec.UDF = 1
+                raise
+
+build = UnitSupport