There is a contrast between vague and clear throughout "How it Happened." Briefly, list things which are vague and things which are clear."How it happened" by conan doyle
In this story, the narrator goes into a great deal of detail about the car and its workings. He also is quite clear about the details of the physical environment. He is much more vague about matters of the mind and emotion.
Having read the story, you will know quite a bit about the car. You know how the gears work. You know how the gears work on his other car. You know how steep the hill is and how many curves there are. You know exactly how high the wheel went up the bank and you know which part of the car hit which part of the gate when they finally crash.
But you know very little about the feelings of anyone involved. You have the sense that Perkins is devoted to the narrator. He is willing to risk his life for him. But even this is vague. Beyond that, you have no knowledge of who the narrator is or what he is thinking. You do not have a good, detailed description of what he thinks or feels as the car speeds down the hill.