In a Sunday strip, Calvin was playing outside when he started being pulled up into the sky. He escaped by grabbing hold of a passenger airplane, and it took him very far before he regained normal gravity. In a weekday strip, Calvin explained his failed homework assignment by claiming that his parents were behind on the gravity bills and so, gravity-deprived, Calvin was unable to work.
This plot point was reused in a story arc, where Calvin's gravity reversed as he was about to start doing his homework, and he was as such unable to complete his assignment.
Also, in a single weekday strip, gravity became completely absent in Calvin's house.