This an oscillating marquee, that contains an internal mechanism that rotates the marquee from the neutral position shown, to +45 degrees, reverses back through neutral to -45 degrees, then reverses back again to the neutral position.  The window gives visibility to a cycle counter, that keeps track of the overall marquee revolution count.  To see the internal mechanism of this assembly, click this link to go the the Gear and Crank Assembly – Open page.

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