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Seiko C153-5007

Seiko's first calculator watch


The pace of digital technology advancements in the 1970s was truly astounding. From the very digital wristwatch in 1972 which displayed only the time, it was just 5 years until multi-function digital calculator watches were released. Released in 1978, model C153 was Seiko's very first calculator watch and it's astounding that they got pretty much everything right from the start.

The Seiko C153 has an 8 digit calculator display which is located above the main time display and doubles as the date and seconds display when the watch is not in calculator mode. To enter calculator mode, press the middle button on the right side. The calculator features addition, subtraction, multiplication and division using floating point arithmetic along with a square root function and memory recall. The bottom button is used to activate the backlight and the top button is used only when setting the watch. To set the watch, pull out the middle button (which is a little confusing until you know the trick).

Calculator watches were the hot new item for a short period in history from early 1976 to about 1978. The very first calculator watch was the Pulsar model 901, which was released right before Christmas 1975 for the astounding price of $3950. It had an 18 kt gold case and it was rumoured that President Ford wanted one but that Betty vetoed the idea. A year later, Pulsar introduced a more affordable stainless steel version for "only" $550. A few other models were released around the same time:

  • Hewlett-Packard's HP-01 scientific calculator watch
  • Hughes' chunky calculator watch which was later used as a prop in the TV series "Battlestar Galactica"
  • Citizen's round calculator watch with buttons around the perimeter of the watch face
  • Uranus' super rare calculator watch, of which almost none are still working today.

In many ways, the Seiko C153 was the best of them all! Unlike most other calculator watches of the era, it was so well engineered that most of them are still working today. It features a modern and very readable LCD display (with backlight). Even better, the buttons are easy to press and don't require the use of a sylus like the Pulsar and HP models. In fact, HP planned to build successor to their HP-01 with raised keys like the Seiko but the project never made it past the prototype phase. The Seiko is also an almost perfect size and weight, thinner than the chunky Hughes and smaller than the attractive but massive HP-01.

The C153 was not only Seiko's first calculator watch, it was their best calculator watch. In some ways, the Seiko C153 was ahead of its time. The C153 model is not as sought after as some of the other calculator models listed above partially because it still looks contemporary almost 40 years later. WIthout knowing that it is a 1970s era watch, you could easily mistake it for a modern remake.

However, the build quality of the Seiko is much better than the inexpensive calculator watches of today. The case is all metal and the stainless steel bracelet is very well constructed, sturdy, lightweight, and comfortable. Also, the keys are metal instead of rubber or plastic. It's a very well engineered and constructed wristwatch.


Case: Very good.
The case has only a few very faint signs of wear. The front and sides of the case are excellent. The highly polished sides have only the finest hairline scratches. The case back is the only place where evident signs of wear are visible. There are scratches on the case back and battery cover from careless replacing of the batteries. However, from the front, the watch looks almost new.

Face / Hands: Excellent.
The face is in excellent condition, almost mint.

Crystal: Excellent.
The crystal looks like glass but is actually some type of hardened acrylic. It has been repolished to be almost perfectly clear and smooth.

Band / Bracelet: Excellent.
The original stainless steel bracelet is super well constructed and is in excellent, almost mint condition.

Function / Accuracy: Excellent.
All functions work perfectly, including the bright backlight. All calculator buttons work properly and are easy to press. Digital quartz accuracy.