Limited Edition of 88 Pieces. Frederique Constant Watch Tourbillon Perpetual Calendar Limited Edition FC-975N4H6. The Frederique Constant watches Perpetual Calendar Tourbillon Manufacture model is presented in a substantial 42mm diameter 3 part case, available either in polished stainless steel or in 18K rose gold. Both come with a see through case back to let one admire the delicate Perlage & Cotes de Geneve decorations. The watches feature a stunning, skeletonized silver colour dial with navy blue sub dials and outer ring and a navy blue alligator strap.