G'day,
disclaimer first, you´ll not get to see any shiny new stuff here. Only boring old stuff around.
And not one many enthusiasts would consider a nice example, probably:

Sometimes spending long hours in the office makes people do crazy things 
Admittedly this time it´s been a popular online auction (*gasp*) AND i ended up with a piece not being exactly Haute Horlogerie on first sight:

What did catch on me was the fact this little 'ol ticker is cased in 18K yellow gold, something likewise uncommon for the GP models of that (mid 1960´s) time.
It´s not a very large watch, but quite thin for it´s age. This may not be very uncommon too, but it´s been exactly this case design to awake some memories.
And since you didn´t move on by now, i guess i can continue to bother
Which may lead us to a suspense story; old stuff can bring a surprise or two.
First of all, GP didn´t do that many 18K units in those years and particularly not with a one-piece case.
So with the new finding in hands, a comparison promised to be helpful:


Well yes, that´s apparently the same case. Same dimensions, same material....
So we´re looking at the only model offered by GP with this case, in a period of roughly 2 years between 1965 and 1968 only.

And while the outer impression is less than promising, the brethren unveil some hidden inner values:


In fact Girard-Perregaux was the only brand world-wide to offer an Observatory Chronometer.
Like the "Observatoire", it´s been tested by the Observatory Neuchatel and underwent the hardest 45-day precision timing of it´s time.
Reportedly ony a few thousand wrist watch movements were submitted to the Chronometer Trials ever, which makes all a pretty uncommon beastie.
But the fact GP submitted movements out of serial production, with a year-long fine tuning of each individual movement before the tests, really took the cake then. No other brand dared to offer an Observatory-certified chronometer for sale in a watch actually made to be worn on a daily base, so one may understand how genuinely shocking the new technology of GP´s fast-beat movements inside must have been to the watch world. Subsequently, the Observatory Neuchatel granted the Centennial Prize to Girard-Perregaux (the only award of this kind ever issued).
So this little watch, fitted with a poorly restored dial, seems to be more special than first view may promise.
And i´m quite confident it came with a nice certificate (or in precision watchmaking, a "bulletin") like it´s brothers then:
Girard-Perregaux reserved this elegant thin case variant of their Observatory Chronometer model, of which only a few dozen was made, exclusively for the US markets. Hence it´s not found that often and easily overlooked. Yet it´s quite special and in some way paved the way for modern watchmaking, as the fast beat rate later was adapted to today´s standard of 28.800 A/h.
I think this little one will be subject of a bit more research - and a full spa treatment in GP´s Service Department.
And then, to find the way back to the initial opening, i´m sure it will bring late pleasure for long days in the office. Or a collector´s obsession, depending on how you put it
Greetings from Germany,
Peter