Zaratsu is Grand Seiko's hand polishing technique: the case is held against the flat face of a rotating metal disc, producing a mirror surface with no distortion while keeping the sharp ridge where two planes meet. Ordinary buffing rounds those edges. First used in the 1960s around the 44GS, it is what makes the Grand Seiko Style possible.
Mechanical watches are rated in seconds per day (Seiko's 6R35: +25/−15 s/day), quartz in seconds per month (Seiko 8T63: ±15 s/month; Grand Seiko 9F: ±10 s/year), solar is quartz powered by light instead of a battery, and Spring Drive is a mainspring watch regulated by a quartz crystal at ±15 s/month. Pick by what you want from ownership, not by rank.
Eco-Drive is Citizen's light-powered quartz technology: a solar cell (under the dial, or ring-shaped around it) charges a lithium secondary cell, so there is no battery to replace. Citizen states a full charge runs more than six months in darkness, and select models with power save run up to seven years. It changes the power supply, not the timekeeping.
Spring Drive is Seiko's hybrid movement: a mechanical mainspring supplies all the power (no battery), while a quartz crystal vibrating at 32,768 Hz provides the timing reference. Its Tri-synchro regulator replaces the escapement with an electromagnetically braked glide wheel, producing a silent, continuously gliding seconds hand. Standard 9R calibers keep time to about ±1 second per day (±15 seconds per month).
