My automatic watch has gain / loss time and it is now not time accurate.

The accuracy of mechanical / automatic watches may not fall within the specified range of time accuracy because loss / gain changed due 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.

Please go through the following checks, as your watch might be affected by nearby magnetism and temperature which may temporarily or lose time or stop operating:

Have you placed your watch at the following magnetic products that may affect your watch?

1. Cellular phone (speaker)
2. Bag with magnet buckle
3. AC-powered shaver
4. Portable radio (speaker)
5. Magnetic cooking device eg. Microwave oven, induction cooker
6. Magnetic health belt
7. Magnetic necklace
8. Magnetic health mat
9. Magnetic health pillow
10. Television
11. Staying near high voltage power lines 
12. any electrical products that emits magnetic field

Please keep the watch more than 10cm away from magnetic products.

Have you placed your watch at an extreme temperature area?

The parts that compose the accuracy of mechanical / automatic 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 / automatic watches tend to lose time at high temperatures while they tend to gain time at low temperatures.

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 the 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.