To me the week always starts on Monday; using the same shard FM database, some of my Mac clients get Monday on the left hand column but others get Sunday. Any idea how to change this? - I guess it is the OS not FM?

Yes, it's the OS. Change Formats in System Preferences >International to UK vs. US.

No - I tried that - all my clients are on UK setting. I still get Sunday as the first day of the week!?

Well back in the day we used to have to save clones of our files to get them to permanently use the system formats. If your file is one that was originally created in an old version of FileMaker that may be a factor.

Also, is your file hosted or single user? When you say "clients" do you mean multiple users on the same server?

There's a "Set Use System Formats" script step, you could experiment with that.

As an test, I created a new file with a date field set as Drop-down Calendar. My system is set to US, and the week starts on Sunday. I changed the Region in International/Formats to UK, and the week starts on Monday.

So the System Preferences is definitely a factor, but apparently in your case there is something more going on.

i have a related problem and your hint on the older fm version was enlightening, because indeed i have problems with files that were originally created in (and are still running under) FMD6. i am in germany, but my system is in english.

so i created the same test file in FMD6 and FMA10 with just a single date field to auto-enter the current date. the v6 file displays dd.mm.yyyy. the v10 file displays mm/dd/yyyy.

on my previous mac g4 with the same settings, the FMD6 files would always display mm/dd/yyyy.

how come the default settings (or system formats) have changed?