An alignment means of a measurement instrument includes a housing an optical component having a principal axis in a direction parallel to a desired alignment; a first light source positioned at a first distance S1 from the optical component and at a first height h1 from the principle axis; a second light source positioned at a second distance S2 from the optical component and at a second height h2 from the principle axis; and an angle barrier means arranged between the optical component, and the first and second light sources. 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′; and block visibility of the second light source along the principal axis at a distance smaller than d2, wherein d2 is smaller than d1′.