I make these from 3mm birch plywood. The clock is battery operated and the calendar is in two (2) parts: A wheel with the year and days of the week that you manual rotate and a stationary disc that has the dates of the day. Engraved into the stationary disc are the leap years also, which months have 30 and 31 days and February has 28 except in a leap year then has 29. I only make the calendar clock for an order.