Most (non-computer) perpetual calendars do not render good representations of a month.  For example, see http://www.photo-dictionary.com/photofiles/list/1717/2276perpetual_calendar.jpg and http://chestofbooks.com/crafts/scientific-american/sup4/images/PERPETUAL-CALENDAR.png. Some show the month with a variable starting day of the week. Others show the month with the maximum number of days instead of the actual number of days in the month. In general, they usually require a complicated table lookup to determine how to set the calendar view. 

This calendar attempts to address this by:

1) Eliminating table lookups by providing viewports that show only relevant information.

2) Providing an accurate representation of a month, always starting with Sunday and showing only the days that actually exist in the month.

3) Providing a logical process for setting the calendar: set the year, set the month, set the starting day of the month, then mask off the days that don't appear in that month.

The calendar is double sided to reduce the diameter of the overall calendar.  A single sided version could be created by putting the year and month information on outer rings. That was my initial design, but it got too big, and I was hoping to create a smaller, pocketable version like some of the older ones. See http://en.wikipedia.org/wiki/File:50yearcalendar.JPG.

This calendar would be easy to convert to laser cut and laser etched metal sheets, which would yield a keepsake that would work for more than a century. Replacing the year disk would make it work for another century.

<p>I've made one using a descendent of your design. My version removed the outer masks and made the viewports output only.</p><p>https://www.instructables.com/id/Perpetual-Calendar-200-Years/</p>
<p>Thank you for this, it is really useful!</p>
<p>HGJ - You should also use Disk 4 right above the calendar disk. This masks off the right number of days (for Feb 2016, it is 29). Just a suggestion.</p>
<p>I also have tutorials make perpetual calendar (used until 2050), the simplicity of this friend.</p>
<p>OMG. This is the best calendar I've found in the internet. thank you so much.</p>
Great calendar! I am developing a series of activities/models for Mathematics of Planet Earth (http://mpe2013.org is the official website and my own is http://zeal-mpe.com). I would like to provide your pdf files on my website so that my readers can download them easily. I will obviously give full credit to you and the model will be available freely for all users. I trust that would be OK. <br>Sitaram
Where do you want me to send the files? I will send you PDFs with the polar grids removed.
Can you email them to me? b.r.sitaram@gmail.com. I am planning to package them into a single pdf along with the instructions so that my users can download them easily. <br> <br>After seeing your instructable, I designed a couple of perpetual calendars, which i will upload in a few days time. <br> <br>Thanks! Sitaram
Sure, I could provide the PDFs. They are attached to the Instructible. I could include the Excel file that I used to create the data represented in the calendar. That was probably the most enlightening part of the project.
Cool calendar!
Interesting design, you could produce it in serie, and market it.

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