It seems that many Swiss watch owners refuse to take their movements and watches in to be serviced by professionals. They seem to believe that accuracy can be achieved by adjusting the regulator screw +/- without a timing machine. It’s better that you either take your watch in for a proper service or just live with losing or gaining a few seconds each day. If your watch is losing a lot of time you need a proper cleaning/service.
Regulating ETA swiss movement is a lot more complex than it appears. If your watch is inaccurate beyond factory tolerance there is a reason. The watch probably requires cleaning, conditioning, oiling, greasing and inspection. You need to have a professional ensure that all of the wheels are free from obstruction. The hairspring must be centered and the last coil of the hairspring must move freely between regulator pins.
A timing machine is then used to regulate the properly serviced and conditioned watch to provide accuracy within the parameters of the particular ETA movement.