Looking over the model wall

An original literary non-fiction-style account of trying a simple periscope at an interactive exhibition.

The wall was only a model, but I objected to not seeing over it. It had been built precisely for that purpose. A small sign invited visitors to use the periscope, which I regarded as a rather elaborate answer to a problem the exhibition had created for itself.

I put my eye to the opening. At first I saw a bright patch of ceiling. An attendant asked me to turn the tube slightly. The ceiling slid away, and a small scene appeared beyond the wall: a bench, a painted tree and a red cup on a table. I had not moved my feet. This seemed an unfair amount of travel for such a minor adjustment.

My daughter asked for a turn. I told her to wait while I examined the arrangement properly. She said that I had been examining a cup for quite a long time. I moved aside. She turned the tube, looked, turned it again and asked why the scene was unfinished at the edges. I had not seen the edges. I had been too pleased with my new access to wonder what had been left outside it.

When I tried again, I found the painted tree stopped before it reached the floor. A strip of unpainted board supported the bench. The view was still clear, but clarity now seemed a much smaller claim than completeness. My daughter asked whether we could look from the other side without the periscope. I said that this would be a useful comparison, which allowed me to follow her without admitting that she had thought of it first.

How does the writer use language to make the narrator's changing confidence humorous?