April 29 1936 Hans Wilsdorf accomplished one of his dreams ie to have 500 prince movements certified chronometers by the Observatory.
These movements were numbered from 501 to 1000 and were all certified with the mention "excellent".
Why a dream? Wilsdorf had these movement produced to sell 500 Prince watches at the occasion of the Jubilee of King George V.
I believe that you have what remains of that serie of watches as they all were bearing the word "Onservatory" on the dial.