PATEK PHILIPPE | A PINK GOLD OPENFACE WATCH WITH GUILLAUME BALANCE AND PHOTOCOPY OF BULLENTIN OF MARCHE, MADE IN 1905 | 百達翡麗 | 粉紅金懷錶，備Guillaume擺輪及時計證書副本，機芯編號152678，錶殼編號257664，約1905年製

This pink gold openface Patek Philippe pocket watch may look simple in its appearance, however on closer inspection of its movement, the watch is regulated by a guillaume balance. The term guillaume comes after its inventor, a French doctor by the name of Guillaume. Guillaume steel is alloy with nickel to reduce its coefficient of expansion. Brass and Guillaume steel rims change the radius of gyration of the balance to follow the requirement of the change in elasticity of the balance spring more closely. Meaning, the middle temperature error is reduced to half a second in 24 hours. Thus, making watches fitted with a Guillaume balance more costly to make, however, much more accurate.