Owner manual / English
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Casio Module 681 Manual
Two owner's manual PDFs for the Casio module 681, each a different scan (English included). Casio's spec sheet lists one SR721SW, with 3 years of battery life and accuracy within ±30 seconds a month; the module first shipped in Aug 1987.
Module specs
Battery: SR721SW (silver-oxide)
Rated battery life: 3 years
Rated accuracy: ±30 sec/month
Casio service manual ref: S/M-253
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