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.