From: James Redin
Hello Victor, I asked about your request to a firend of mine who distributes Casio in Australia. Got this answer that hope will be useful for you:
I will see if I can find any instructions for the old watch. I was never very big with watch sales.
All Casio watches are set by a similar method. A button is held in for a few seconds and the display should start flashing on one of the digits. Either the same button or an alternative button will advance the display to the selected number. Press the initialisation button once and the second digital should start flashing. The process is repeated until all digitals are sampled.
This is usually written on the case near the button. If I find anything I will let you know
You may find a pointer to his Casio site in the MODERN CALCULATORS section of my X-Number site.
The X-Number World of Calculators