Spotter: secret places

A little bit crazy professor Slain having an ill luck invented a time machine. He knew how to invent it, but he does not know how to control it!

Every time he travels in time he notices some small changes which influence the appearance of his house and the surroundings.

Help him to find these distinctions, in case professor succeeds to guess how they are connected he probably will be able to stabilize the dimensional warp and will learn to control his journeys.