I came across this thread in the vintage forum about a member who bought a vintage Rolex Prince that was rebranded as a Gruen for the US market. The best part about it is that he had no idea of its history or value.
Some info on the watchThe duo-dial "Doctor's Watch' movement was the invention of Aegler S.A. of Bienne, supplier of movements to Rolex (now part of Rolex). Gruen also owned shares in Aegler, whose factory was across the street from Gruen's own Precision Factory. This expensive watch, the first production movement to obtain regular chronometer certification without special individual adjustment, was accordingly sold in the British Empire and Europe exclusively as the Rolex Prince, and in the USA exclusively as the Gruen Techni-Quadron, so they never competed. This started in 1928 and continued until 1934 when Gruen sold its shares in Aegler, ending production of the Terchni-Quadron version of the watch. Rolex could thereafter distribute in the USA, although it did not do so in a big way till the '40s.