I have acquired a Citizen Crystron LC (1977) model 50-1310, Case No 4-096363K. It has a Zero-Set button on the lower left of the case, a top right Light, a middle right Select, and a lower right Read/Set buttons. When I press the recessed Select button to set the time & date, the flashing-digit(s) sequence is the following: seconds, minutes, hour, month, date, day, and the last one is a single digit on the top right of the LCD screen that can be set to either 0, 1, 2, or 3. My question is what is that last setting? Any help would be appreciated as I cannot find the instructions for this model on the web.