If one watch explains why the PRX became a phenomenon, it is the Tissot PRX Powermatic 80 with a black dial. It takes the sharp, integrated-bracelet design Tissot first launched in 1978 and adds a modern Swiss automatic movement, the kind of combination that used to cost several times more.

The black dial is the most versatile in the range: its fine waffle texture adds depth without color, and the polished indexes and hands stand out cleanly. The Powermatic 80 movement at its heart is the real upgrade over the quartz PRX. It winds itself with the motion of your wrist, stores up to 80 hours of energy, and uses Tissot's patented Nivachron balance spring for resistance to magnetism and temperature swings. Flip the watch over and you can watch it working through the see-through caseback.

At 40mm wide and under 11mm thick, it slides under a cuff for the office and is just as comfortable on weekends. If you only own one PRX, this is the one that goes with everything.

Specs: PRX Powermatic 80 40mm Black, T137.407.11.051.00

• Case: 40mm 316L stainless steel, 39.5mm lug to lug, 10.93mm thick
• Lug width: 12mm; weight about 138 g
• Movement: Swiss automatic Powermatic 80, Nivachron balance spring
• Power reserve: up to 80 hours
• Dial: black with waffle texture, index markers, Super-LumiNova hands, date
• Crystal: sapphire, antireflective on the underside; exhibition caseback
• Water resistance: 100 meters
• Bracelet: integrated steel, quick-release, push-button butterfly clasp

The benchmark PRX: black, automatic and ready for anything.