Hi, I'm new here but I have been looking around for information regarding my vintage Casio digital watches and it seems this may be the most promising place to find answers.
To give you a bit of my background, by way of introduction: my first few watches, when I was growing up, were digital Casios. One was even some sort of calculator watch with completely flat panel. It stood out because all the other boys' calculator watches had little rubber buttons. All those early watches are now either lost or deep in the bottom of storage boxes, now. These days I have a handful of modern Casios that remind me of my old watches (A168, CA-53W, DBC-611), though the main focus of my collection, in more recent times, has in the realms of High Accuracy Quartz watches. That is to say, watches that either through thermocompensation or thermoinsensitivity can achieve accuracy of better than 20 seconds per year. Although I have examples of most types of high accuracy quartz watch, I have now fine-tuned my collection to focus on rare 4.19 MHz watches, and this is where Casio comes back into the picture.
Watches with 4.19 MHz oscillators are less sensitive to climatic changes than watches with the standard 32 kHz oscillator. The first such watch was Citizen's Crystron 4 Mega, released in 1975 - a year after Omega released their 2.4 MHz Marine Chronometer. Whereas the Omega was spec'd to 12 seconds per year, the Citizen was rated at 3 seconds per year. For one reason or another, 4.19 MHz watches didn't catch on and besides the Citizen watches, the only such niche watch known to the high accuracy WIS world was the 1978 Junghans MegaQuarz. That was until relatively recently, when a 4.19 MHz Casio emerged.
Either in the very late 1970s or (more likely) in the very early 1980s, Casio produced three models containing Module 75. These models were the SP-400, the SP-410 and the SP-400G. The SP-400 and the SP-410 were both spec'd to 15 seconds per year, whilst the SP-400G was spec'd to 10 seconds per year. Module 75 includes a trimmer capacitor for fine-tuning the rate, so as to keep the watch on-spec over time.
Since learning about these watches, I have managed to identify only two of each model, out there on the Web. Here are the three (NOS!) that I have been lucky enough to add to my collection:
SP-400
SP-410
SP-400G
All together
The watches themselves are fairly unremarkable. They have the light, stopwatch and date functions that you'd expect but are otherwise special only in their accuracy. I have tried to find out as much about these watches as possible, but one thing I don't know is the date of production. It has been speculated that these watches were most likely sold in either 1980 or 1981, but I cannot find any information on any vintage watch forum about these watches or about Module 75.
So... has anyone heard of these watches or of Module 75? Would anyone be able to shed any more light on their production date(s) or the extent of their release (I'm guessing they were JDM)?
To give you a bit of my background, by way of introduction: my first few watches, when I was growing up, were digital Casios. One was even some sort of calculator watch with completely flat panel. It stood out because all the other boys' calculator watches had little rubber buttons. All those early watches are now either lost or deep in the bottom of storage boxes, now. These days I have a handful of modern Casios that remind me of my old watches (A168, CA-53W, DBC-611), though the main focus of my collection, in more recent times, has in the realms of High Accuracy Quartz watches. That is to say, watches that either through thermocompensation or thermoinsensitivity can achieve accuracy of better than 20 seconds per year. Although I have examples of most types of high accuracy quartz watch, I have now fine-tuned my collection to focus on rare 4.19 MHz watches, and this is where Casio comes back into the picture.
Watches with 4.19 MHz oscillators are less sensitive to climatic changes than watches with the standard 32 kHz oscillator. The first such watch was Citizen's Crystron 4 Mega, released in 1975 - a year after Omega released their 2.4 MHz Marine Chronometer. Whereas the Omega was spec'd to 12 seconds per year, the Citizen was rated at 3 seconds per year. For one reason or another, 4.19 MHz watches didn't catch on and besides the Citizen watches, the only such niche watch known to the high accuracy WIS world was the 1978 Junghans MegaQuarz. That was until relatively recently, when a 4.19 MHz Casio emerged.
Either in the very late 1970s or (more likely) in the very early 1980s, Casio produced three models containing Module 75. These models were the SP-400, the SP-410 and the SP-400G. The SP-400 and the SP-410 were both spec'd to 15 seconds per year, whilst the SP-400G was spec'd to 10 seconds per year. Module 75 includes a trimmer capacitor for fine-tuning the rate, so as to keep the watch on-spec over time.
Since learning about these watches, I have managed to identify only two of each model, out there on the Web. Here are the three (NOS!) that I have been lucky enough to add to my collection:
SP-400
SP-410
SP-400G
All together
The watches themselves are fairly unremarkable. They have the light, stopwatch and date functions that you'd expect but are otherwise special only in their accuracy. I have tried to find out as much about these watches as possible, but one thing I don't know is the date of production. It has been speculated that these watches were most likely sold in either 1980 or 1981, but I cannot find any information on any vintage watch forum about these watches or about Module 75.
So... has anyone heard of these watches or of Module 75? Would anyone be able to shed any more light on their production date(s) or the extent of their release (I'm guessing they were JDM)?