diff --git a/tools/fuzzy-30003-matcher.py b/tools/fuzzy-30003-matcher.py
new file mode 100755
index 0000000..255166a
--- /dev/null
+++ b/tools/fuzzy-30003-matcher.py
@@ -0,0 +1,204 @@
+#!/usr/bin/env python3
+
+#
+# Regression testing helper: takes a 3.0.5 port-30003 output file
+# and a 3.1.0 port-30003 output file and generates a diff, after
+# dealing with the known formatting / data differences
+
+import csv
+from contextlib import closing
+
+horizon=5
+
+def fuzzy_match_details(l1, l2):
+    _, _, type1, _, _, addr1, _, _, _, _, _, cs1, alt1, gs1, hdg1, lat1, lon1, vr1, sq1, change1, emerg1, spi1, aog1 = l1
+    _, _, type2, _, _, addr2, _, _, _, _, _, cs2, alt2, gs2, hdg2, lat2, lon2, vr2, sq2, change2, emerg2, spi2, aog2 = l2
+
+    if addr1 != addr2:
+        return (False, 'adr')
+
+    if type1 != type2:
+        # 3.0.5: reports DF17 surface/airborne with no position as type 7
+        # 3.1.0: reports DF17 surface/airborne with no position as type 2/3
+        if type1 != '7':
+            return (False, 'typ')
+        if type2 != '2' and type2 != '3':
+            return (False, 'typ')
+        if lat1 != '' or lon1 != '':
+            return (False, 'typ')
+
+    if alt1 != alt2:
+        # 3.0.5: omits altitude in DF17 if no position was decoded
+        # 3.1.0: includes it
+        if type1 != '7' or alt1 != '' or alt2 == '':
+            return (False, 'alt')
+
+    if gs1 != gs2:
+        # 3.0.5: truncates computed GS
+        # 3.1.0: rounds computed GS
+        if gs1 == '' or gs2 == '' or abs(int(gs1) - int(gs2)) > 1:
+            return (False, 'gs ')
+    if hdg1 != hdg2:
+        # 3.0.5: truncates computed heading
+        # 3.1.0: rounds computed heading
+        if hdg1 == '' or hdg2 == '':
+            return (False, 'hdg')
+        delta = abs(int(hdg1) - int(hdg2))
+        if delta > 180:
+            delta = 360 - delta
+        if delta > 1:
+            return False
+
+    if lat1 != lat2:
+        return (False, 'lat')
+    if lon1 != lon2:
+        return (False, 'lon')
+    if vr1 != vr2:
+        return (False, 'vr ')
+
+    if sq1 != sq2:
+        # 3.0.5: strips leading zeros
+        # 3.1.0: preserves leading zeros
+        if ('0' + sq1) != sq2 and ('00' + sq1) != sq2 and ('000' + sq1) != sq2:
+            return (False, 'sqk')
+
+    # 3.1.0: only reports these when available
+    if change1 != change2:
+        if change1 != '0' or change2 != '':
+            return (False, 'chg')
+    if emerg1 != emerg2:
+        if emerg1 != '0' or emerg2 != '':
+            return (False, 'emg')
+    if spi1 != spi2:
+        if spi1 != '0' or spi2 != '':
+            return (False, 'spi')
+
+    if aog1 != aog2:
+        # 3.1.0: different rules for when AOG is reported
+        if aog1 != '' and aog2 != '':
+            return (False, 'aog')
+
+    return (True, None)
+
+def fuzzy_match(l1, l2):
+    return fuzzy_match_details(l1, l2)[0]
+
+def fuzzy_match_reason(l1, l2):
+    return fuzzy_match_details(l1, l2)[1]
+
+def next_line(reader, queue):
+    if queue:
+        return queue.pop()
+    line = next(reader, None)
+    if line is None or len(line) == 0:
+        return None
+    else:
+        return [reader.line_num] + line
+
+def unpush_line(queue, line):
+    queue.insert(0, line)
+
+def csv_diff(path1, path2):
+    diffs = []
+    q1 = []
+    q2 = []
+
+    with closing(open(path1, 'r')) as f1, closing(open(path2, 'r')) as f2:
+        r1 = csv.reader(f1)
+        r2 = csv.reader(f2)
+
+        l1 = next_line(r1, q1)
+        l2 = next_line(r2, q2)
+
+        while (l1 is not None) or (l2 is not None):
+            if l1 is None:
+                yield ('+', None, l2)
+                l2 = next_line(r2, q2)
+                continue
+
+            if l2 is None:
+                yield ('-', l1, None)
+                l1 = next_line(r1, q1)
+                continue
+
+            if fuzzy_match(l1, l2):
+                yield (' ', l1, l2)
+                l1 = next_line(r1, q1)
+                l2 = next_line(r2, q2)
+                continue
+
+            #print('mismatch:', l1, l2)
+
+            save_1 = []
+            save_2 = []
+
+            found = False
+            for i in range(horizon):
+                next_l2 = next_line(r2, q2)
+                if next_l2 is not None:
+                    if fuzzy_match(l1, next_l2):
+                        # skip l2 and any lines in save_2
+                        # continue with l1 and next_l2
+                        yield('+', None, l2)
+                        for l in save_2:
+                            yield('+', None, l)
+                        l2 = next_l2
+                        q1.extend(reversed(save_1))
+                        found = True
+                        break
+                    else:
+                        save_2.append(next_l2)
+
+                next_l1 = next_line(r1, q1)
+                if next_l1 is not None:
+                    if fuzzy_match(next_l1, l2):
+                        # skip l1 and any lines in save_1
+                        # continue with next_l1 and l2
+                        yield('-', l1, None)
+                        for l in save_1:
+                            yield('-', l, None)
+                        l1 = next_l1
+                        q2.extend(reversed(save_2))
+                        found = True
+                        break
+                    else:
+                        save_1.append(next_l1)
+
+            if found:
+                #print('new l1:', l1)
+                #print('new l2:', l2)
+                #print('new q1:')
+                #for q in q1: print(q)
+                #print('new q2:')
+                #for q in q2: print(q)
+                continue
+
+            #print('lookahead: nothing likely')
+
+            q1.extend(reversed(save_1))
+            q2.extend(reversed(save_2))
+            yield ('*', l1, l2)
+            l1 = next_line(r1, q1)
+            l2 = next_line(r1, q2)
+
+def format_line(line):
+    line_num = line[0]
+    subrow = line[1:3] + line[5:6] + line[11:]
+    return str(line_num) + ': ' + ','.join(subrow)
+
+if __name__ == '__main__':
+    import sys
+    for action, old, new in csv_diff(sys.argv[1], sys.argv[2]):
+        if action == ' ':
+            if False: print ('      ' + format_line(new))
+        elif action == '*':
+            reason = fuzzy_match_reason(old, new)
+            print ('< ' + reason + ' ' + format_line(old))
+            print ('> ' + reason + ' ' + format_line(new))
+        elif action == '-':
+            # 3.0.5: emits lines for all-zero messages
+            # 3.1.0: doesn't
+            if old[5] != '000000':
+                print ('-     ' + format_line(old))
+        elif action == '+':
+            print ('+     ' + format_line(new))