Method of measuring the accuracy of at least one timepiece, particularly a mechanical watch, comprising at least one visual display device, and where one of said at least one visual display devices of said timepiece is selected as the experimental display, characterized in that: - at the request of the user, a first theoretical image of the display position is generated by an image generator coupled to an internal or external time reference source; - at the request of the user, said first theoretical image of the display position is modified in order to synchronise said display position of said first modified image with the real display of said experimental display of said timepiece. - a first instant with which said experimental display is in a first display position corresponding to said first modified image, measured in correspondence with said time reference source, is stored, said first display position being synchronised in optical comparison to the time display position of said timepiece with said first modified image, with the user altering the position of said first image as desired to synchronise said first image with said real timepiece display, and a first display value is determined corresponding to said first modified image, said first display value is stored in a storage means in correlation with said first instant; - after a determined time interval following said first instant, - at the request of the user, a second theoretical display position image is generated by said image generator; - at the request of the user, said second theoretical display position image is modified to synchronise said display position of said modified second image with the real display of said experimental display of said timepiece; - a second instant with which said experimental display is in a second display position corresponding to said second modified image, measured in correspondence with said time reference source, is stored, said second display position being synchronised in optical comparison to the time display position of said timepiece with said second modified image, with the user altering the position of said second image as desired to synchronise said second image with said real timepiece display, and a second display value is determined corresponding to said second modified image, said second display value is stored in a storage means in correlation with said second instant; - the time difference displayed between said second display value and said first display value is calculated; - the variation in rate of said experimental display is calculated, and said variation in rate is displayed on a viewing means. - at the request of the user, a first theoretical image of the display position is generated by an image generator coupled to an internal or external time reference source; - at the request of the user, said first theoretical image of the display position is modified in order to synchronise said display position of said first modified image with the real display of said experimental display of said timepiece. - a first instant with which said experimental display is in a first display position corresponding to said first modified image, measured in correspondence with said time reference source, is stored, said first display position being synchronised in optical comparison to the time display position of said timepiece with said first modified image, with the user altering the position of said first image as desired to synchronise said first image with said real timepiece display, and a first display value is determined corresponding to said first modified image, said first display value is stored in a storage means in correlation with said first instant; - after a determined time interval following said first instant, - at the request of the user, a second theoretical display position image is generated by said image generator; - at the request of the user, said second theoretical display position image is modified to synchronise said display position of said modified second image with the real display of said experimental display of said timepiece; - a second instant with which said experimental display is in a second display position corresponding to said second modified image, measured in correspondence with said time reference source, is stored, said second display position being synchronised in optical comparison to the time display position of said timepiece with said second modified image, with the user altering the position of said second image as desired to synchronise said second image with said real timepiece display, and a second display value is determined corresponding to said second modified image, said second display value is stored in a storage means in correlation with said second instant; - the time difference displayed between said second display value and said first display value is calculated; - the variation in rate of said experimental display is calculated, and said variation in rate is displayed on a viewing means.