Calibre 990

Notes

The 990 was an attempt to keep the benefits of two mainspring barrels for decreasing the strain on drive train components while also significantly decreasing the thickness of the calibre by mounting the barrels on the same plane rather than co-axially on top of one another. The 990 was the last in-house mechanical calibre Longines designed produced and it would continue to be used at least into the mid 1980s. It remains the thinnest automatic, center seconds and date calibre ever produced even as of 2026 at 2.95mm. It's closest competitors are the JLC 899 (3.3mm) and 920 (3.4mm) as well as the Horage K2 (3.3mm).