This watch dates from December 1981 with the serial number 1D1536.
Extract from Pieter Doensens excellent book The only watch with this display ever produced in commercial quantities, was the ECD F623A by Seiko. The function is based on an electro-chemical process of the deposition (oxidation-reduction) of tungstentrioxide on the electrodes when the electrical current is flowing in one direction, and the removing of this material when the current is flowing in the opposite way. This process is comparable to the process of plating / deplating. In contrast with the field effect display, this display has a higher power dissipation and shows greater unreliability in the long term. The advantage is that the digits stay visible, even when no voltage is applied. The production stopped after two years.

WATCHES WITH MODULE F623

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