Croton, Nivada, or Nivada Grenchen: by whatever name they go by, these watches were meant to handle anything. No model of Nivada's typifies this more than the Chronomaster Aviator Sea Diver. Not only is it a chronograph (a chronomaster, even), it can be used at sea and in the air. 

Nivada (called Croton in the U.S. due to a copyright dispute with Movado, because "Nivada" clearly sounds like "Movado") introduced the Chronomaster Aviator Sea Diver in 1963 and produced it until 1978. It came in many different flavors throughout its fifteen-year run. The most common iteration, featured on this watch, has two chronograph registers at 3 and 9 o'clock, and later versions had the addition of a date window. The registers are black on black, with a red triangle in the 30 minute subdial for timing regattas. Nivada used broad arrow hands during the 1960s before transitioning to stick hands in the 1970s; it's the latter style that you see here. 

The Chronomaster also used many different movements, from the Valjoux 92 and 7733 to the Landeron 248. Ours has the venerable Valjoux 23, that column-wheel movement that powered chronographs by Rolex and Heuer, among others. With 18,000 bph and a smooth action, the Valjoux 23 remains superlative. 

Another salient feature of this watch: the bi-directional bezel, showing 60-minute elapsed time as well as a GMT function. Because, as you can guess from the name, this was meant to be a dive watch as well. Another nod to the diving heritage is the engraving on the case back, which denotes water resistance up to 20 ATM. 

While these watches are by no means scarce, one in this condition--and with a box--is rare indeed. The bevels on the lugs are as sharp as they must have been when this watch first rolled off the assembly line. The hour markers and hands do show signs of age, having mellowed to a handsome even patina, and the case back likewise shows signs of light use. But what we have here is a versatile timepiece, at home in any environment you wish to wear it.