P1992年古代发明系列100元地动仪银币 NGC PR69。eoples Republic of China. Inventions & Discoveries Seismograph platinum 100 Yuan 1992 PR69 Ultra Cameo NGC, one of the five platinum pieces issued in Series 1, KM413. An extremely rare issue with a mintage of 500 pieces each for the 5 platinum types. This spectacular example has no apparent flaws! The fields are deeply mirrored, and the devices so frosted they have a sand-blasted appearance.