Trisector of Kempe The linkage is made up of three similar contra-parallelograms ABCD, ADEF, AFGH , where the point A is pivoted on the plane (their sides are proportional and two couples of contra-parallelograms have the same angle ); in every position their angles are equal and so the bars DA and FA divides the angle BAH in three equal parts. In our laboratory there are also the trisectors with two squares and the trisector of Pascal (see fig.).