Index: sodar/trunk/sodar/data.py
===================================================================
--- sodar/trunk/sodar/data.py (revision 67)
+++ sodar/trunk/sodar/data.py (revision 68)
@@ -60,4 +60,5 @@
 import re
 import numpy as n
+import datetime
 
 class Data(list):
@@ -112,5 +113,6 @@
         self._copy()
         self._convert()
-        # compute time interval
+        self._stamp()
+        self._timeInterval()
         # correct for missing times
         # compute minium altitude
@@ -134,6 +136,5 @@
         INVALID = "-9999"
         for sample in self.samples:
-            body = sample[1]
-            for altitude in body:
+            for altitude in sample['body']:
                 for key,value in altitude.items():
                     try:
@@ -143,4 +144,44 @@
                     except (ValueError, TypeError, KeyError):
                         altitude[key] = n.NaN
+            for key,value in sample['header'].items():
+                try:
+                    if value == INVALID:
+                        raise ValueError
+                    sample['header'][key] = int(value)
+                except (ValueError, TypeError, KeyError):
+                    sample['header'][key] = n.NaN
+    
+    def _stamp(self):
+        """Add a datetime stamp to each sample."""
+        for sample in self.samples:
+            try:
+                header = sample['header']
+                sample['stamp'] = datetime.datetime(header['YEAR'],
+                                                    header['MONTH'],
+                                                    header['DAY'],
+                                                    header['HOUR'],
+                                                    header['MIN'])
+            except (KeyError, TypeError):
+                sample['stamp'] = datatime.datetime.min
+    
+    def _timeInterval(self):
+        """Add a time interval attribute"""
+        intervals = zip([sample['stamp'] for sample in self.samples[:-1]],
+                        [sample['stamp'] for sample in self.samples[1:]])
+        intervals = [interval[1] - interval[0] for interval in intervals]
+        accumulator = {}
+        for interval in intervals:
+            if interval in accumulator:
+                accumulator[interval] += 1
+            else:
+                accumulator[interval] = 1
+        maxVotes = max(accumulator.values())
+        for key,value in accumulator.items():
+            if value == maxVotes:
+                self.timeInterval = key
+                break
+        self.timeInterval = getattr(self,
+                                    'timeInterval',
+                                    datetime.timedelta.resolution)
 
 
@@ -176,6 +217,7 @@
     
     def _copy(self):
-        """Create a deep copy as a tuple of header and body copies."""
-        return (self.header._copy(), self.body._copy())
+        """Create a deep copy as a dictionary of header and body copies."""
+        return {'header':self.header._copy(),
+                'body':self.body._copy()}