The lengths of the links comply with the condition: A͞C=C͞B=C͞E-C͞D. Links 3 and 4 have pins a that slide in slots b of rules 2 and 1. The slot width equals the pin diameter. In any fixed position of rule 2 the edge of rule 1 is parallel to the edge of rule 2.
$988$LG,4L$