diff --git a/logdif.py b/logdif.py
new file mode 100644
index 0000000..1a790f2
--- /dev/null
+++ b/logdif.py
@@ -0,0 +1,102 @@
+"""compare commits of logs in different branches
+
+selecting the time range is based on file 'sync_branches'
+which should be in the branch where logdif.py is running
+"""
+
+import sys
+from subprocess import check_output
+
+branches = sys.argv[1:]
+
+commits = {}
+log_no = {}
+log_title = {}
+cursor = {}
+
+since_info = []
+
+with open("sync_branches") as f:
+    # a file containing
+    #  YYYY-mm-dd <branch1> <branch2>
+    # for each date the branches are synced
+    for line in f:
+        if line.strip():
+            info = line.split()
+            if set(branches) & set(info[1:]) == set(branches):
+                since_info.append(info[0])
+
+gitlog = ['git', 'log', '--oneline']
+if since_info:
+    since = sorted(since_info)[-1]
+    print(f'commits since {since}')
+    gitlog.append(f'--since-as-filter={sorted(since_info)[-1]}')
+else:
+    print(f'no info for {branches} found in file sync_branches')
+
+for br in branches:
+    cursor[br] = 0
+    output = check_output(gitlog + [br])
+    log_title[br] = bytitle = {}
+    log_no[br] = byno = []
+    no = 0
+    for line in output.decode('utf-8').split('\n'):
+        if line:
+            hash, title = line.split(' ', 1)
+            bytitle.setdefault(title, []).append([(no, hash)])
+            byno.append([hash, title])
+            no += 1
+
+
+# find matches
+for br, byno in log_no.items():
+   for no, line in enumerate(byno):
+      commits.setdefault(line[1], {}).setdefault(br, []).append((no, line))
+
+ordered = {}
+for title, info in commits.items():
+    # sort the info dict by value
+    ordered[title] = {b: v for v, b in sorted((v, b) for b, v in info.items())}
+
+commits = ordered
+
+cnt = [0]
+
+def print_commit(line):
+    if not line[1]:
+        return  # title cleared: this line is already printed
+    # print and mark line as already printed
+    info = commits[line[1]]
+    output = []
+    title = line[1]
+    for br in log_no:
+       infolist = info.get(br)
+       if infolist:
+           no, iline = infolist.pop(0)
+           if not infolist:
+               info.pop(br)
+           output.append(f'{no:3}:{iline[0]}')
+           iline[1] = ''  # clear title
+       else:
+           output.append(' ' * 11)
+    print(' '.join(output), title)
+    cnt[0] += 1
+    if cnt[0] % 50 == 0:
+        input(f' {br0:11s} {br1:11s}')
+
+
+(br0, log0), (br1, log1) = list(log_no.items())
+no1 = 0
+for no0, line0 in enumerate(log0):
+    if line0[1]:  # line not yet printed
+           infodict = commits[line0[1]]
+           if len(infodict) > 1:  # found a match
+               info0 = infodict[br1]
+               # loop over commits in br1 until matched no
+               no1end = info0[0][0]
+               if no1end > no0:
+                   for n in range(no0, no1end):
+                       line1 = log1[n]
+                       print_commit(line1)
+                   no1 = no1end
+           print_commit(line0)
diff --git a/sync_branches b/sync_branches
new file mode 100644
index 0000000..2c4cdf5
--- /dev/null
+++ b/sync_branches
@@ -0,0 +1,2 @@
+2024-01-29 wip develop
+