I'm still confused about what was actually being done and why. Like what's the purpose of this experiment? What are the outputs, what does a successful result l

I'm still confused about what was actually being done and why. Like what's the purpose of this experiment? What are the outputs, what does a successful result look like and what does a failure look like? So I take it that positioning the reflector over the plutonium core generates more or less output from the sphere. Was somebody measuring that? But if so surely the actual precise distances involved are important? So if the point is "how close do we have to get to get to X output", then surely distance measuring is of critical importance, and a screwdriver is completely unsuitable for that task. Now I get it was a demonstration, so the actual data output may not have been important. But still, the person you're teaching needs the actual useful results when they do the experiment for real, so surely they will need something other than a screwdriver?