Method for deducing geometrical defects of an optical article turning machine configured for machining ophthalmic lenses by using a lens machining tool acting in three directions (16, 17, 18) in said turning machine, characterized in that the method comprises the steps of manufacturing three checking pieces and receiving data representative of characteristics of said checking pieces and also a defect value deducing step, during which at least one geometrical defect value is deduced based at least on an indicative information of an optical and/or geometrical data related to an optical and/or geometrical characteristic of the checking pieces; - said step of manufacturing comprises, successively, in any order, the steps of manufacturing a first checking piece according to a first predetermined theoretical geometry at a first height in said turning machine, manufacturing a second checking piece according to a second predetermined theoretical geometry different from said first predetermined theoretical geometry, at a second height in said turning machine, and manufacturing a third checking piece according to a third predetermined theoretical geometry different from said first predetermined theoretical geometry and from said second predetermined theoretical geometry, at a third height in said turning machine, distinct from said first height and second height; - said step of receiving data comprises the step of measuring optical and/or geometrical data representative of optical and/or geometrical characteristics of each of said first checking piece, second checking piece and third checking piece; and - said defect value deducing step comprises the step of deducing, from said measured optical and/or geometrical data, a perpendicular defect value (dperp) of said turning machine, according to a first direction and to a second direction amongst said three directions, a calibration defect value (dx) of said turning machine, according to said first direction, and a parallelism defect value (dpara) of said turning machine, according to said first direction. - said step of manufacturing comprises, successively, in any order, the steps of manufacturing a first checking piece according to a first predetermined theoretical geometry at a first height in said turning machine, manufacturing a second checking piece according to a second predetermined theoretical geometry different from said first predetermined theoretical geometry, at a second height in said turning machine, and manufacturing a third checking piece according to a third predetermined theoretical geometry different from said first predetermined theoretical geometry and from said second predetermined theoretical geometry, at a third height in said turning machine, distinct from said first height and second height; - said step of receiving data comprises the step of measuring optical and/or geometrical data representative of optical and/or geometrical characteristics of each of said first checking piece, second checking piece and third checking piece; and - said defect value deducing step comprises the step of deducing, from said measured optical and/or geometrical data, a perpendicular defect value (dperp) of said turning machine, according to a first direction and to a second direction amongst said three directions, a calibration defect value (dx) of said turning machine, according to said first direction, and a parallelism defect value (dpara) of said turning machine, according to said first direction.