The watchmaker tells you what the standard error is?

Due to the structural properties of the winding mechanism, materials, friction and fatigue, the output torque between the rings changes from strong to weak, as well as friction torques like those generated by the winding and gears during transportation, all affect the accuracy of the clock's timekeeping. In addition climate temperature, gravity, magnetic field, local environment and location also affect the normal operation of spring pendulum clocks. Now quartz watches overcome the weakness of mechanical watches by utilizing the extremely stable vibration frequency of quartz crystals as a time reference. 

Quartz watch running time error is generally ± 0.5s (superior), mechanical watch running time range error ± 15s/d - ± 120s/d