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You've really done some excellent testing here. To be honest I'm not exactly sure what is the root cause of the issue here whether it's still a timing problem or if there is something more sinister like an issue with the actual sync code itself. I'll be trying to replicate your issues with it over the next several days. If anyone else can report about success or failure please let me know. Especially with the iOS products.

My suggestion would be to turn off all syncing and manually use the URL to retrieve the file. Verify that you can retrieve every 9 minutes. If not, then either the 9 minute limit isn't working, or there's still something syncing that you haven't found and turned off.

I am trying to write a program which will regularly (once a day) downfile the .ics file and compare it with the prior downloaded file and report the differences (new events, changed events, removed events).

Does anyone know if the once per hour download time is per device or once per unique weblink?

The reason I am asking if because I use the link for both my Google Calendar, in iOS and also through my program and if the download of once per hour for all my devices/programs then its a problem for me as I cant know when the other devices last did an update.

kennethjorgensen wrote:Does anyone know if the once per hour download time is per device or once per unique weblink?

The limit is not once per hour -- it is once per 9 minutes. But it is indeed a limit for the link. If Device A accesses the sync URL at 10:00, then no other device can access it until after 10:09; if Device B then accesses it at 10:10, then no other device can access it until after 10:19, etc.

Thanks for the clarification. I will have to think about how to tackle that.

I'd suggest a twofold strategy:

1) Minimize the number of calls made by various devices. You don't have control over Google calendar, but I find it to be about once a day. I assume you can set the frequency in iOS.

2) Have your program detect a failed result and try again in 9 minutes.

Thanks Russell, nice to see my thoughts written up

I think its my iPad I need to update much less frequent as even putting the link into the browser only returns a file sometimes and the same is the case in .NET where it returns a null most times.