Perpetual calendar frames come with a set of inserts that can be arranged to show the proper days and dates of the month. Unfortunately this set is not complete, but regardless, no one uses it for that purpose nowadays. It's almost always used a a picture frame. It's a  lovely part of any nice Tiffany Grapevine desk set. This example has a rich, green-brown patina with no cracks in any of the glass panels. It's properly signed on the back, TIFFANY STUDIOS NEW YORK 940 and measures 6¼" x 7¼".