Professionals state that an imported mechanical watch can be regarded as “accurate” with a daily deviation of ±60 seconds. According to the Swiss chronometer certification system (C.O.S.C.), a mechanical watch earns chronometer certification when its daily deviation falls between -4 and +6 seconds. The stricter Geneva Seal allows a tolerance of -3 to +2 seconds per day. As long as the error stays within a reasonable range and is predictable and adjustable, it is acceptable. If the error exceeds reasonable limits, the watch has a fault and should first be tested and diagnosed by a mechanical timing tester. In addition, regarding the timekeeping error of various watches, the current industry standards stipulate:

For Calendar Mechanical Watch Type I (Men’s Watch), the instantaneous timekeeping error ranges are as follows: High-grade products have a 24-hour error of -30 ~ +45 seconds; Grade I products have a 24-hour error of -40 ~ +75 seconds; Qualified products have a 24-hour error of -60 ~ +105 seconds. The continuous running duration for all grades is no less than 36 hours.

For Calendar Mechanical Watch Type II (Midsize Watch), the instantaneous timekeeping error ranges are: High-grade products have a 24-hour error of -35 ~ +65 seconds; Grade I products have a 24-hour error of -50 ~ +95 seconds; Qualified products have a 24-hour error of -70 ~ +135 seconds. The continuous running duration for all grades is no less than 35 hours.

For Calendar Mechanical Watch Type III (Ladies’ Watch), the instantaneous timekeeping error ranges are: High-grade products have a 24-hour error of -40 ~ +85 seconds; Grade I products have a 24-hour error of -60 ~ +115 seconds; Qualified products have a 24-hour error of -80 ~ +165 seconds. The continuous running duration for all grades is no less than 34 hours.

For Automatic Mechanical Watch Type I (Men’s Watch), the instantaneous timekeeping error ranges are: High-grade products have a 24-hour error of -20 ~ +30 seconds; Grade I products have a 24-hour error of -30 ~ +60 seconds; Qualified products have a 24-hour error of -50 ~ +90 seconds. The continuous running duration for all grades is no less than 36 hours.

For Automatic Mechanical Watch Type II (Midsize Watch), the instantaneous timekeeping error ranges are: High-grade products have a 24-hour error of -25 ~ +50 seconds; Grade I products have a 24-hour error of -40 ~ +80 seconds; Qualified products have a 24-hour error of -60 ~ +120 seconds. The continuous running duration for all grades is no less than 30 hours.

For Automatic Mechanical Watch Type III (Ladies’ Watch), the instantaneous timekeeping error ranges are: High-grade products have a 24-hour error of -30 ~ +70 seconds; Grade I products have a 24-hour error of -50 ~ +100 seconds; Qualified products have a 24-hour error of -70 ~ +150 seconds. The continuous running duration for all grades is no less than 28 hours.

Quartz watches are not classified by types. Their instantaneous timekeeping error ranges: High-grade products have a 24-hour error of -0.5 ~ +0.5 seconds; Grade I products have a 24-hour error of -1.0 ~ +1.0 seconds; Qualified products have a 24-hour error of -1.5 ~ +1.5 seconds.

It can be seen from the above standards that quartz watches deliver superior timekeeping accuracy due to electronic control. Mechanical watches rely on mechanical oscillation principles for timekeeping and thus have relatively lower precision. Besides, larger mechanical watches tend to achieve better accuracy; conversely, smaller ones have lower precision.