A method for adjusting a timepiece including: providing a portable object including a screen and a camera; testing accuracy of a piece of time information of the timepiece by using the camera of the portable object to compare with a piece of time information obtained from an external source; sending the time information from the portable object to the timepiece if a difference is detected, the timepiece including at least one phototransistor arranged at a case for receiving the time information, the timepiece to display the correct time information, the sending including: defining on the screen of the portable object an area of shape and dimensions similar to the case of the timepiece; holding the case of the timepiece against the area; sequentially displaying black or white in the area, in a sequence of black and white corresponding to a luminous coding of the time information.