I thought I’d feature this 6138-7000 because it’s a variation of Seikos twin register chronograph that isn’t seen very often. It’s unusual in as much as it has a slide rule bezel and indicator much like the contemporary Breitling Navitimers, although quite how pilots were meant to operate it whilst flying a plane I’m not entirely sure! This example came in for a bit of a smarten up and a full movement service.

The caseback indicates a production date of June 1972.

Once I’d removed the back I could see the movement was complete and in reasonable shape.

With the movement uncased the dial and handset appeared to be in cracking condition.

I soon removed those which revealed the day/date disks, again in good shape.

With those removed along with the date changeover wheel and a couple of plates the top chronograph plate could be removed.

This reveals the 12hr register wheel and reset/start levers along with the keyless work.

With the lever work removed it just leaves the keyless work to go….

….which didn’t take too long.

I could then turn the movement over to start on the chronograph/motion work.

Here the train wheel bridge is ready for removal.

The stripped components were then sent for a trip through the cleaning machine.

Whilst the cleaner was running I turned my attention to the case parts. The watch arrived with a better case and bezel, a NOS crystal and an original plastic indicator ring. These are very difficult to source these days!

The case, pushers, springs and crown were all ultrasonically cleaned….

….then new seals were fitted along with the crystal and indicator ring and the case was now ready for the movement.

After the movement parts were cleaned the inspection turned up a shattered top barrel arbor jewel, this component is critical as the 12hr register is run directly from a wheel located on the arbor, any lateral movement would play havoc with the reset.

I had an old top plate with a good jewel which I managed to remove without cracking it! This meant the jewel was a direct fit and no adjustment of the plate was necessary. The old jewel was pressed out of the plate with my Seitz tool.

The old and the replacement compared.

The jewel was pressed home flush with the plate, again using the Seitz jewelling tool Here is a shot of the old donor plate and the transplanted jewel in place in the new one.

The jewel in its new home.

Reassembly could now start beginning with the mainspring.

The motion work and chronograph layer are ready for the bottom chronograph plate to be fitted in this shot.

And here the plate, pallets and balance work is all reinstalled. The movement can now be demagnetised and roughly timed.

On the other side reassembly started with the keyless work….

….then the 12hr chronograph levers and wheel….

….the top chronograph plate is next, note the top barrel arbor jewel and its proximity to the hour register pinion.

The day/date disks were next….

….followed by the dial and handset.

The movement was recased then the autowind mechanism and oscillating weight were refitted….

….which meant my work was done. I have to say this is a cracking example of Seikos little seen twin register chronograph ‘slide rule’.

And a shot with the chronograph running.