This is the Seiko QUF101G Pendulum Clock: an art deco magnetic pendulum clock from the 80s that puts on a show as you let it run. It gets going with a simple nudge. You can attach and remove the pendulum arm easily. These clocks were made in various designs. Most of them are rare these days but can still be found on eBay.
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Seiko QUF101G Swinging Magnetic Pendulum Clock -- Gadgetify
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