The lengths of the links comply with the conditions: A͞C=D͞B and A͞D=C͞B. Flexible link 2, secured at point E to link 3, runs over link 1. Link 1 is of special shape, enabling weighing to be performed with a single constant weight a. When, in weighing, point E of link 3 turns about fixed axis D to position E', link 1 turns about fixed axis F to position 1' and weight a is moved to position a'.
$2017$FL,B$