The accuracy of mechanical watches is indicated by the “daily rate.”
The accuracy of mechanical watches may not fall within the specified range of time accuracy because loss/gain changes according to the position of the watch, which is dependent on the conditions of use, such as the length of time during which the watch is worn on the wrist, arm movement, and whether the mainspring is wound up fully or not, etc.
The loss/gain of mechanical watches is not measured by a daily rate, but by daily rates of one week or so.
Accuracy variation according to temperature
The parts that compose the accuracy of mechanical watches are made of metals. It is well known that metals expand or contract depending on temperatures due to metal properties. This exerts an effect on the accuracy of the watches. Mechanical watches tend to lose time at high temperatures while they tend to gain time at low temperatures.
Mainspring wound condition and accuracy
In order to improve accuracy, it is important to regularly supply energy to the balance that controls the speed of the gears. The driving force of the mainspring that powers mechanical watches varies between when fully wound and immediately before it is unwound. As the mainspring unwinds, the force weakens.
Relatively steady accuracy can be obtained by wearing the watch on the wrist frequently for the self-winding type and winding up the mainspring fully everyday at a fixed time to move it regularly for the wind-up mechanical type.
Effect of magnetism
When affected by a strong magnetism from outside, the mechanical watch may lose/gain time temporarily. The parts of the watch may become magnetized depending on the extent of the effect.
In such a case, consult the retailer from whom the watch was purchased since the watch requires repair including demagnetizing.