The Day‑Nite series was introduced in the early 1960s as a civilian evolution of the jump‑disc technology first showcased in the 1958 Gruen Airflight, an instrument originally developed for U.S. Air Force pilots.
While the Airflight displayed a dramatic 12‑to‑24‑hour numerical jump, the Day‑Nite model explored a more elegant and artistic interpretation:
- a rotating internal disc
- two contrasting sets of hour markers
- an automatic color change every 12 hours (daytime black → nighttime radium green)
This complication is exceptionally rare in the vintage market and represents one of Gruen’s most creative mechanical experiments.
The 510 CA / 510 RSS references are considered the definitive Day‑Nite variants, distinguished by their open‑window dial architecture and the dedicated N510CA movement.
A very nice example of this rare watch. New dark army green nato strap.