The Citizen Caliber 0100, introduced in 2019, is an Eco-Drive light-powered quartz watch that Citizen rates at an accuracy of plus or minus one second a year. It uses a quartz crystal oscillating at 8.4 MHz, far above the 32,768 Hz of normal quartz watches, and a slim titanium case. I could not confirm the case diameter from a primary source, so it is not stated.

Citizen described it as the most accurate watch in the world, a claim that refers to annual accuracy for a wristwatch. The movement is among the thinnest of its type and is powered by light, so it does not need a battery change.

It was well covered as a technical landmark for quartz watchmaking, and a continuation of Citizen’s high-precision tradition. Early production was limited, and I could not confirm whether it is still on sale, so the production status is left blank.