Abstract: The invention relates to a measuring and/or plotting and/or sighting instrument (1) comprising a first marker (8a), a second marker (8b), a third marker (8c) and a fourth marker (8d) linked together by a link element (10) allowing a relative displacement of the markers according to the following formula: d ? ? 1 d ? ? 2 = d ? ? 1 d ? ? 6 = ? with: d1 being the distance between the first and fourth markers; d2 being the distance between the second and fourth markers; d6 being the distance between the first and third markers; and ? being a constant number, notably ? is equal or substantially equal to 1.5 or 1.6 or 1.62 or 1.618 or (1+?5)/2.