Measured: Accuracy is stated in seconds per day for mechanical movements and seconds per month for quartz. A COSC certified chronometer must run within minus 4 and plus 6 seconds a day.
The basics
What to know about watch movement
Movement answers two questions that listings blur together. Automatic, quartz and solar describe what powers and regulates the watch. Chronograph names an added stopwatch function that can sit on top of either. Digital names the display, since a digital watch is quartz regulated underneath. Separating those is the first step.
Accuracy has a stated convention. Mechanical watches are rated in seconds gained or lost per day. A chronometer certified by COSC must run between minus 4 and plus 6 seconds a day. Quartz is rated per month, and an ordinary quartz movement holds around 15 seconds a month, roughly twenty times closer than a good automatic. Power reserve, the time a mechanical watch runs unworn, is stated in hours.
Choose by what you are willing to do. Quartz, solar and digital ask nothing between battery or service intervals. An automatic asks to be worn or wound, reset when it stops, and serviced every five to ten years. In return it gives you a mechanism you can watch working.
