diff --git a/SimPEG/Survey.py b/SimPEG/Survey.py
index 2d2a5a00..1ed649db 100644
--- a/SimPEG/Survey.py
+++ b/SimPEG/Survey.py
@@ -200,6 +200,7 @@ class Fields(object):
 
     knownFields = None
     txPair = BaseTx
+    dtype = float
 
     def __init__(self, mesh, survey, **kwargs):
         self.survey = survey
@@ -207,6 +208,10 @@ class Fields(object):
         Utils.setKwargs(self, **kwargs)
         self._fields = {}
 
+    def _storageShape(self, nP):
+        nTx = self.survey.nTx
+        return (nP, nTx)
+
     def _initStore(self, name):
         if name in self._fields:
             return self._fields[name]
@@ -219,13 +224,31 @@ class Fields(object):
               'F':  self.mesh.nF,
               'E':  self.mesh.nE}[loc]
 
-        nTx = self.survey.nTx
-        field = np.empty((nP, nTx))
+        if type(self.dtype) is dict:
+            dtype = self.dtype[name]
+        else:
+            dtype = self.dtype
+        field = np.empty(self._storageShape(nP), dtype=dtype)
 
         self._fields[name] = field
 
         return field
 
+    def _txIndex(self, txTestList):
+        if type(txTestList) is slice:
+            ind = txTestList
+        else:
+            if type(txTestList) is not list:
+                txTestList = [txTestList]
+            for txTest in txTestList:
+                if not isinstance(txTest, self.txPair):
+                    raise KeyError('First index must be a Transmitter')
+                if txTest not in self.survey.txList:
+                    raise KeyError('Invalid Transmitter, not in survey list.')
+
+            ind = np.in1d(self.survey.txList, txTestList)
+        return ind
+
     def _indexAndNameFromKey(self, key):
         if type(key) is not tuple:
             key = (key,)
@@ -239,19 +262,7 @@ class Fields(object):
         if name is not None and name not in self.knownFields:
             raise KeyError('Invalid field name')
 
-        if type(txTestList) is slice:
-            ind = txTestList
-        else:
-            if type(txTestList) is not list:
-                txTestList = [txTestList]
-            for txTest in txTestList:
-                if not isinstance(txTest, self.txPair):
-                    raise KeyError('First index must be a Transmitter')
-                if txTest not in self.survey.txList:
-                    raise KeyError('Invalid Transmitter, not in survey list.')
-
-            ind = np.in1d(self.survey.txList, txTestList)
-
+        ind = self._txIndex(txTestList)
         return ind, name
 
     def __setitem__(self, key, value):
@@ -289,7 +300,6 @@ class Fields(object):
         return out
 
 
-
 class BaseSurvey(object):
     """Survey holds the observed data, and the standard deviations."""
 
@@ -492,7 +502,3 @@ class BaseSurvey(object):
     # def phi_d_target(self, value):
     #     self._phi_d_target = value
 
-
-if __name__ == '__main__':
-    d = BaseData()
-    d.dpred()