Nov -2014: The above two chronographs are prototypes for the Double O version of the Offshore Professional, so called because of the circular day and date windows.  I built six; 3 with each dial type (left and right chronographs above have dials from different colour pallets).  Double O went into production in March 2015 with just a couple of small changes from these prototypes.


The Field Engineer went through an extensive prototyping and testing phase.  The prototypes carried standard Valjoux 7750 movements instead of custom movements, with cases from a test production run.  Testing included high pressure oily and salt water resistance, drop and shock impacts, chemical resistance and temperature cycling.  The final prototype was fitted with a Field Engineer customised movement and went to a charity auction in support of an Angolan orphanage.
Traditionally the weakest components in a chronograph are the push buttons and crown.  Thanks to large seatings the Field Engineer push buttons and crown can withstand significant amounts of impact energy.
Pressure testing the prototypes was done with a full immersion pressure chamber to high pressures in a workshop with thick walls; my 'ice house' workshop.  Built around 1790, the ice house has been used for everything from storing winter ice to keep G&T's cool in summer, to being an air raid shelter in the London Blitz. Collapse pressure of the chronograph is a little over 30ATM.

For the production Chronographs I use a different pressure chamber and test each case to 160 psi and then hold at 120 psi.  160 psi is 110 m water depth, 11 barg pressure (12 bara), 12 atm, or 360 feet water depth.  Despite the water proof depth, the Field Engineer is not suitable for diving.  A diving watch needs a screw down crown and locking push-buttons, instead of the floating crown tube and push button designs I use for impact and dust resistance.

Protection against fine dust is far more difficult that providing water resistance as dust doesn't evaporate away, and with incorrect sealing will slowly penetrate as you cycle the buttons or pull the crown to adjust the timing.  The above pictures are from the final round of real world dust testing at the top of the Namib Desert in Southern Angola, with an ambient temperature of 42 Centigrade (108 Fahrenheit).  The dust here is as fine as talcum powder, but becomes incredibly abrasive once mixed with a little water or sweat.  

Any colour you like, as long as it's Panatone 426. The hands are not black, but slightly off black.  Similarly the dial is not white, but cream. Coloured sweep second hands are not an option, just experimenting

The above picture clearly shows the stainless steel 3rd layer of the dial.  The inner and outer diameters of this layer fit a Fibonacci ratio, as does the colour contrast to the cream enamel of the second layer.  The 3rd layer is electrically continuous with the outer case Faraday cage and  encompasses some of the more magnetically sensitive components of the Valjoux movement.  The sapphire crystal 'display' back does not reduce the Faraday cage effect as your skin is sufficiently electrically conductive to complete the cage. 


Quality, Strength, Performance