The lengths of the links comply with the condition: A͞B=B͞C. Freely suspended at point B is a pendulum with a bob of weight G. Due to this weight, slider 3 is displaced in its guides from the extreme right-hand position, shown by the dash lines, to the left, overcoming force P which equals P=(G/2)tan(α) where α is one half of the angle between links 1 and 2.
$1502$SC,4L$