I decided today that since he was starting to eat and he likes to sit up that I would get out the highchair. I dug it out of the storage in the basement and brought it up to the living room to put it together. When I was about halfway through Grandma Walter showed up to visit. She was surprised by how big Calvin has gotten.
After I got the highchair together I put Calvin in it and attached the toy it came with. He loves it. It plays music and lights up. I also got out his stacking cups for him to play with. He really likes them. I need to baby-proof the house soon he is starting to become very mobile. He scoots himself all around on his belly.
EDIT: Calvin also rolled from back to front for the first time today!