Seiko

No doubt the 7C series is an excellent movement for diving. However, as the first digit of the movement number goes up, the movement specs and finishing improve. Thus a 9F is roughly two steps higher than a 7C. I can't speak for how Seiko spaces or defines the "steps".

Take a look at the 7C movement (plastic and stamped metal) and its numbers:

Here is the Seiko spec sheet for the 7C46 movement family:

2. Loss/gain (monthly rate).............Less than 15 seconds at normal temperature range (5° C ~ 35° C) (41° F ~ 95° F) 

3. Operational temperature range..–10° C ~ +60° C (14° F ~ 140° F) 

4. Driving system.............................Step motor, 1 piece 

5. Display system 

 Time...................................................Three hands (Hour, minute and second hands) 

 Day.....................................................Displayed in letters (or Kanji characters)

 Date...................................................Displayed in numerals 

6. Battery............................................5 years 

7. Water Tested (atmospheres of pressure) 

 600M..................................................75 bar 

 1200M................................................125 bar 

8. Helium gas tested .........................Yes

Now compare to the 9F series used in the Grand Seiko (mine needed a battery anyway   and the new battery is STRAIGHT UP, not crooked like this one!):

2. Loss/gain (ANNUAL rate)..............±10 seconds on the wrist 8 hours per day within a normal temperature range (5° C ~ 35° C) (41° F ~ 95° F).

    Loss/gain (monthly rate)...............Approximately 2 seconds depending on conditions.

7. Water Tested (atmospheres).........not specified

8. Helium gas tested .........................not specified

You can see the timekeeping is substantially better on the 9F family, and my thought is that this is because they carefully age, sort and grade the quartz crystals, using only the best ones for 9F models. However the 7C movement is specially tested to operate under diving conditions.

The typical Seiko quartz movement costs your watchmaker about $20, while the 7C46 costs him about $110 and the price of the 9F isn't public (spare parts for GS generally not distributed outside Seiko).

Here's the watch that got the battery change. The applied Star on the dial indicates that it has one of the limited, specially-tweaked movements rated at +/- 5 seconds a year.

Thanks for asking - I hope this helps answer your query.

Cazalea

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