Calvin In Quarter-Inch Form is a minor alter ego of Calvin's. He appeared in a single Sunday strip.
In it, Calvin had "mysteriously shrunk to a quarter of an inch tall". Just like Calvin In Inch-Tall Form, he tried to alert his parents of his condition. To do so, he took a picture of himself by crawling onto a camera, setting the self-timer, and hanging onto the lens.
Calvin In Quarter-Inch Form was analogous to Calvin misusing his father's camera.