What does 10k RPG mean on Elgin Pocket Watch?

The term "10k RPG" on an Elgin pocket watch indicates that the case is made of a gold-filled material, specifically containing 10 karats of gold. The "RPG" likely stands for "rolled gold plate," which means that a layer of gold is mechanically bonded to a base metal. This designation signifies a level of quality and durability, as the gold layer is thicker than standard gold plating, providing a more luxurious appearance without the cost of solid gold.