diff --git a/galvani/BioLogic.py b/galvani/BioLogic.py
index 78229d7..e644e68 100644
--- a/galvani/BioLogic.py
+++ b/galvani/BioLogic.py
@@ -9,7 +9,7 @@ import csv
 from os import SEEK_SET
 import time
 from datetime import date, datetime, timedelta
-from collections import OrderedDict
+from collections import defaultdict, OrderedDict
 
 import numpy as np
 
@@ -144,119 +144,105 @@ VMPmodule_hdr = np.dtype([('shortname', 'S10'),
                           ('version', '<u4'),
                           ('date', 'S8')])
 
+# Maps from colID to a tuple defining a numpy dtype
+VMPdata_colID_dtype_map = {
+    4: ('time/s', '<f8'),
+    5: ('control/V/mA', '<f4'),
+    6: ('Ewe/V', '<f4'),
+    7: ('dQ/mA.h', '<f8'),
+    8: ('I/mA', '<f4'),  # 8 is either I or <I> ??
+    9: ('Ece/V', '<f4'),
+    11: ('I/mA', '<f8'),
+    13: ('(Q-Qo)/mA.h', '<f8'),
+    19: ('control/V', '<f4'),
+    20: ('control/mA', '<f4'),
+    23: ('dQ/mA.h', '<f8'),  # Same as 7?
+    24: ('cycle number', '<f8'),
+    32: ('freq/Hz', '<f4'),
+    33: ('|Ewe|/V', '<f4'),
+    34: ('|I|/A', '<f4'),
+    35: ('Phase(Z)/deg', '<f4'),
+    36: ('|Z|/Ohm', '<f4'),
+    37: ('Re(Z)/Ohm', '<f4'),
+    38: ('-Im(Z)/Ohm', '<f4'),
+    39: ('I Range', '<u2'),
+    70: ('P/W', '<f4'),
+    76: ('<I>/mA', '<f4'),
+    77: ('<Ewe>/V', '<f4'),
+    123: ('Energy charge/W.h', '<f8'),
+    124: ('Energy discharge/W.h', '<f8'),
+    125: ('Capacitance charge/µF', '<f8'),
+    126: ('Capacitance discharge/µF', '<f8'),
+    131: ('Ns', '<u2'),
+    169: ('Cs/µF', '<f4'),
+    172: ('Cp/µF', '<f4'),
+    434: ('(Q-Qo)/C', '<f4'),
+    435: ('dQ/C', '<f4'),
+    467: ('Q charge/discharge/mA.h', '<f8'),
+    468: ('half cycle', '<u4'),
+    473: ('THD Ewe/%', '<f4'),
+    474: ('THD I/%', '<f4'),
+    476: ('NSD Ewe/%', '<f4'),
+    477: ('NSD I/%', '<f4'),
+    479: ('NSR Ewe/%', '<f4'),
+    480: ('NSR I/%', '<f4'),
+}
+
+# These column IDs define flags which are all stored packed in a single byte
+# The values in the map are (name, bitmask, dtype)
+VMPdata_colID_flag_map = {
+    1: ('mode', 0x03, np.uint8),
+    2: ('ox/red', 0x04, np.bool_),
+    3: ('error', 0x08, np.bool_),
+    21: ('control changes', 0x10, np.bool_),
+    31: ('Ns changes', 0x20, np.bool_),
+    65: ('counter inc.', 0x80, np.bool_),
+}
+
 
 def VMPdata_dtype_from_colIDs(colIDs):
-    dtype_dict = OrderedDict()
+    """Get a numpy record type from a list of column ID numbers.
+
+    The binary layout of the data in the MPR file is described by the sequence
+    of column ID numbers in the file header. This function converts that
+    sequence into a numpy dtype which can then be used to load data from the
+    file with np.frombuffer().
+
+    Some column IDs refer to small values which are packed into a single byte.
+    The second return value is a dict describing the bit masks with which to
+    extract these columns from the flags byte.
+
+    """
+    type_list = []
+    field_name_counts = defaultdict(int)
     flags_dict = OrderedDict()
-    flags2_dict = OrderedDict()
     for colID in colIDs:
-        if colID in (1, 2, 3, 21, 31, 65):
-            dtype_dict['flags'] = 'u1'
-            if colID == 1:
-                flags_dict['mode'] = (np.uint8(0x03), np.uint8)
-            elif colID == 2:
-                flags_dict['ox/red'] = (np.uint8(0x04), np.bool_)
-            elif colID == 3:
-                flags_dict['error'] = (np.uint8(0x08), np.bool_)
-            elif colID == 21:
-                flags_dict['control changes'] = (np.uint8(0x10), np.bool_)
-            elif colID == 31:
-                flags_dict['Ns changes'] = (np.uint8(0x20), np.bool_)
-            elif colID == 65:
-                flags_dict['counter inc.'] = (np.uint8(0x80), np.bool_)
+        if colID in VMPdata_colID_flag_map:
+            # Some column IDs represent boolean flags or small integers
+            # These are all packed into a single 'flags' byte whose position
+            # in the overall record is determined by the position of the first
+            # column ID of flag type. If there are several flags present,
+            # there is still only one 'flags' int
+            if 'flags' not in field_name_counts:
+                type_list.append(('flags', 'u1'))
+                field_name_counts['flags'] = 1
+            flag_name, flag_mask, flag_type = VMPdata_colID_flag_map[colID]
+            # TODO what happens if a flag colID has already been seen
+            # i.e. if flag_name is already present in flags_dict?
+            # Does it create a second 'flags' byte in the record?
+            flags_dict[flag_name] = (np.uint8(flag_mask), flag_type)
+        elif colID in VMPdata_colID_dtype_map:
+            field_name, field_type = VMPdata_colID_dtype_map[colID]
+            field_name_counts[field_name] += 1
+            count = field_name_counts[field_name]
+            if count > 1:
+                unique_field_name = '%s %d' % (field_name, count)
             else:
-                raise NotImplementedError("flag %d not implemented" % colID)
-        elif colID == 4:
-            dtype_dict['time/s'] = '<f8'
-        elif colID == 5:
-            dtype_dict['control/V/mA'] = '<f4'
-        # 6 is Ewe, 77 is <Ewe>, I don't see the difference
-        elif colID in (6, 77):
-            dtype_dict['Ewe/V'] = '<f4'
-        # Can't see any difference between 7 and 23
-        elif colID in (7, 23):
-            dtype_dict['dQ/mA.h'] = '<f8'
-        # 76 is <I>, 8 is either I or <I> ??
-        elif colID in (8, 76):
-            dtype_dict['I/mA'] = '<f4'
-        elif colID == 9:
-            dtype_dict['Ece/V'] = '<f4'
-        elif colID == 11:
-            dtype_dict['I/mA'] = '<f8'
-        elif colID == 13:
-            dtype_dict['(Q-Qo)/mA.h'] = '<f8'
-        elif colID == 16:
-            dtype_dict['Analog IN 1/V'] = '<f4'
-        elif colID == 19:
-            dtype_dict['control/V'] = '<f4'
-        elif colID == 20:
-            dtype_dict['control/mA'] = '<f4'
-        elif colID == 24:
-            dtype_dict['cycle number'] = '<f8'
-        elif colID == 32:
-            dtype_dict['freq/Hz'] = '<f4'
-        elif colID == 33:
-            dtype_dict['|Ewe|/V'] = '<f4'
-        elif colID == 34:
-            dtype_dict['|I|/A'] = '<f4'
-        elif colID == 35:
-            dtype_dict['Phase(Z)/deg'] = '<f4'
-        elif colID == 36:
-            dtype_dict['|Z|/Ohm'] = '<f4'
-        elif colID == 37:
-            dtype_dict['Re(Z)/Ohm'] = '<f4'
-        elif colID == 38:
-            dtype_dict['-Im(Z)/Ohm'] = '<f4'
-        elif colID == 39:
-            dtype_dict['I Range'] = '<u2'
-        elif colID == 70:
-            dtype_dict['P/W'] = '<f4'
-        elif colID == 74:
-            dtype_dict['Energy/W.h'] = '<f8'
-        elif colID == 78:
-            dtype_dict['Cs-2/µf-2'] = '<f4'
-        elif colID == 123:
-            dtype_dict['Energy charge/W.h'] = '<f8'
-        elif colID == 124:
-            dtype_dict['Energy discharge/W.h'] = '<f8'
-        elif colID == 125:
-            dtype_dict['Capacitance charge/µF'] = '<f8'
-        elif colID == 126:
-            dtype_dict['Capacitance discharge/µF'] = '<f8'
-        elif colID == 131:
-            dtype_dict['Ns'] = '<u2'
-        elif colID == 169:
-            dtype_dict['Cs/µF'] = '<f4'
-        elif colID == 172:
-            dtype_dict['Cp/µF'] = '<f4'
-        elif colID == 173:
-            dtype_dict['Cp-2/µF-2'] = '<f4'
-        elif colID == 434:
-            dtype_dict['(Q-Qo)/C'] = '<f4'
-        elif colID == 435:
-            dtype_dict['dQ/C'] = '<f4'
-        elif colID == 467:
-            dtype_dict['Q charge/discharge/mA.h'] = '<f8'
-        elif colID == 468:
-            dtype_dict['half cycle'] = '<u4'
-        elif colID == 469:
-            dtype_dict['z cycle'] = '<u4'
-        elif colID == 473:
-            dtype_dict['THD Ewe/%'] = '<f4'
-        elif colID == 476:
-            dtype_dict['NSD Ewe/%'] = '<f4'
-        elif colID == 479:
-            dtype_dict['NSR Ewe/%'] = '<f4'
-        elif colID == 474:
-            dtype_dict['THD I/%'] = '<f4'
-        elif colID == 477:
-            dtype_dict['NSD I/%'] = '<f4'
-        elif colID == 480:
-            dtype_dict['NSR I/%'] = '<f4'
+                unique_field_name = field_name
+            type_list.append((unique_field_name, field_type))
         else:
-            print(dtype_dict)
             raise NotImplementedError("column type %d not implemented" % colID)
-    return np.dtype(list(dtype_dict.items())), flags_dict, flags2_dict
+    return np.dtype(type_list), flags_dict
 
 
 def read_VMP_modules(fileobj, read_module_data=True):
@@ -352,7 +338,7 @@ class MPRfile:
         else:
             assert(not any(remaining_headers))
 
-        self.dtype, self.flags_dict, self.flags2_dict = VMPdata_dtype_from_colIDs(column_types)
+        self.dtype, self.flags_dict = VMPdata_dtype_from_colIDs(column_types)
         self.data = np.frombuffer(main_data, dtype=self.dtype)
         assert(self.data.shape[0] == n_data_points)
 
@@ -423,8 +409,5 @@ class MPRfile:
         if flagname in self.flags_dict:
             mask, dtype = self.flags_dict[flagname]
             return np.array(self.data['flags'] & mask, dtype=dtype)
-        elif flagname in self.flags2_dict:
-            mask, dtype = self.flags2_dict[flagname]
-            return np.array(self.data['flags2'] & mask, dtype=dtype)
         else:
             raise AttributeError("Flag '%s' not present" % flagname)
diff --git a/tests/test_BioLogic.py b/tests/test_BioLogic.py
index f42e85d..c8bf163 100644
--- a/tests/test_BioLogic.py
+++ b/tests/test_BioLogic.py
@@ -8,7 +8,7 @@ import numpy as np
 from numpy.testing import assert_array_almost_equal, assert_array_equal
 import pytest
 
-from galvani import MPTfile, MPRfile
+from galvani import BioLogic, MPTfile, MPRfile
 from galvani.BioLogic import MPTfileCSV, str3  # not exported
 
 testdata_dir = os.path.join(os.path.dirname(__file__), 'testdata')
@@ -44,6 +44,37 @@ def test_open_MPT_csv_fails_for_bad_file():
         MPTfileCSV(os.path.join(testdata_dir, 'bio_logic1.mpr'))
 
 
+def test_colID_map_uniqueness():
+    """Check some uniqueness properties of the VMPdata_colID_xyz maps."""
+    field_colIDs = set(BioLogic.VMPdata_colID_dtype_map.keys())
+    flag_colIDs = set(BioLogic.VMPdata_colID_flag_map.keys())
+    field_names = [v[0] for v in BioLogic.VMPdata_colID_dtype_map.values()]
+    flag_names = [v[0] for v in BioLogic.VMPdata_colID_flag_map.values()]
+    assert not field_colIDs.intersection(flag_colIDs)
+    # 'I/mA' and 'dQ/mA.h' are duplicated
+    # assert len(set(field_names)) == len(field_names)
+    assert len(set(flag_names)) == len(flag_names)
+    assert not set(field_names).intersection(flag_names)
+
+
+@pytest.mark.parametrize('colIDs, expected', [
+    ([1, 2, 3], [('flags', 'u1')]),
+    ([4, 6], [('time/s', '<f8'), ('Ewe/V', '<f4')]),
+    ([1, 4, 21], [('flags', 'u1'), ('time/s', '<f8')]),
+    ([4, 6, 4], [('time/s', '<f8'), ('Ewe/V', '<f4'), ('time/s 2', '<f8')]),
+    ([4, 9999], NotImplementedError),
+])
+def test_colID_to_dtype(colIDs, expected):
+    """Test converting column ID to numpy dtype."""
+    if isinstance(expected, type) and issubclass(expected, Exception):
+        with pytest.raises(expected):
+            BioLogic.VMPdata_dtype_from_colIDs(colIDs)
+        return
+    expected_dtype = np.dtype(expected)
+    dtype, flags_dict = BioLogic.VMPdata_dtype_from_colIDs(colIDs)
+    assert dtype == expected_dtype
+
+
 @pytest.mark.parametrize('filename, startdate, enddate', [
     ('bio_logic1.mpr', '2011-10-29', '2011-10-31'),
     ('bio_logic2.mpr', '2012-09-27', '2012-09-27'),