. . "FIG. 1 is a drawing showing essential parts in a normal state; FIG. 2 is an exploded perspective view of an adjusting mechanism; FIG. 3 is a perspective view of the adjusting mechanism in contact with an adjusting dial; FIG. 4 is a perspective view of a contact reversing mechanism; FIG. 5( a) is a drawing showing the contact reversing mechanism and a normally opened contact (a-contact) that are in" . .