The stamp is a perpetual calendar that is circular. On the outside, the numbers 01 - 31 are to mark one day - or even several days - in the month.
Perpetual Calendar Date Fill-In Days Week Self-Inking Rubber Stamp Ink Stamper
CatslifePress Rubber Stamp - Date Series – Sumthings of Mine
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Perpetual Calendar Stamp Date Stamp Monthly Calendar Rubber
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Mizushima Stamp] Perpetual Calendar – Baum-kuchen
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perpetual minimalistic calendar - Extraordinary stationery
The Shachihata Connected Number Stamp is a customizable calendar stamp, japanese stationery
The Mizushima Rubber Stamp Perpetual Calendar comes with 11 different parts so that you can create a calendar for any month of the year, forever.
Mizushima Rubber Stamp Perpetual Calendar
Perpetual calendar with all the months and dates listed.
Perpetual Calendar Rubber Stamp