An alignment means of a measurement instrument , the alignment means comprising - a housing ; - an optical component having a principal axis in a direction parallel to a desired alignment, the optical component being configured such that an eye of the user is to be aligned with the principal axis of the optical component; - a first light source positioned at a first distance S1 from the optical component and at a first height h1 from the principal axis; - a second light source positioned at a second distance S2 from the optical component and at a second height h2 from the principal axis; and - an angle barrier means , - a third light source arranged at a third distance S3 from the optical component and at a third height h3 from the principal axis , wherein the optical component comprises a focal point, wherein the first light source, the second light source and the third light source are positioned between the optical component and the focal point; and wherein the housing, the optical component, and the angle barrier means are arranged to: - block visibility of the first light source along the principal axis at a distance superior to d1'; - block visibility of the second light source along the principal axis at a distance smaller than d2, wherein d2 is smaller than d1'; and - block visibility of the third light source along the principal axis at a distance smaller than d3, wherein d3 is greater than d1' and smaller than d2'; and - block visibility of the second light source along the principal axis at a distance superior to d2', wherein d2' is greater than d1 wherein d1', d2, d2' and d3 are distances from the optical component. - a housing ; - an optical component having a principal axis in a direction parallel to a desired alignment, the optical component being configured such that an eye of the user is to be aligned with the principal axis of the optical component; - a first light source positioned at a first distance S1 from the optical component and at a first height h1 from the principal axis; - a second light source positioned at a second distance S2 from the optical component and at a second height h2 from the principal axis; and - an angle barrier means , - a third light source arranged at a third distance S3 from the optical component and at a third height h3 from the principal axis , wherein the optical component comprises a focal point, wherein the first light source, the second light source and the third light source are positioned between the optical component and the focal point; and wherein the housing, the optical component, and the angle barrier means are arranged to: - block visibility of the first light source along the principal axis at a distance superior to d1'; - block visibility of the second light source along the principal axis at a distance smaller than d2, wherein d2 is smaller than d1'; and - block visibility of the third light source along the principal axis at a distance smaller than d3, wherein d3 is greater than d1' and smaller than d2'; and - block visibility of the second light source along the principal axis at a distance superior to d2', wherein d2' is greater than d1 - block visibility of the first light source along the principal axis at a distance superior to d1'; - block visibility of the second light source along the principal axis at a distance smaller than d2, wherein d2 is smaller than d1'; and - block visibility of the third light source along the principal axis at a distance smaller than d3, wherein d3 is greater than d1' and smaller than d2'; and - block visibility of the second light source along the principal axis at a distance superior to d2', wherein d2' is greater than d1 wherein d1', d2, d2' and d3 are distances from the optical component. <EOS>