When I say “perpetual calendar,” this probably isn’t what comes to mind. You’re likely imagining something like the ceramic Royal Oak Perpetual calendar or the more traditional Patrimony Perpetual. But this little desk-top device of the same name is a manual timekeeper that the user sets each morning and then references throughout the day. It’s called a perpetual calendar because, in theory, it will work forever. The Perpetuum Calendar comes to us from 3D-printed design firm OTHR and Spanish designers Studio Yonoh and it’s about as cool a balance spring–free perpetual calendar as you’ll find anywhere.