How well logging tools see the rock. Pick a tool, set the rock and mud, and watch the measurement happen.
How logging tools see the rock
A log is made by a physical measurement: counted gamma rays, slowed neutrons, electrical current or sound. Here you can watch that measurement happen in a cut-away borehole.
Start with the density tool. A radioactive source sends gamma rays into the rock; they scatter off electrons, and two detectors count those that come back. Change the rock, add mudcake or barite, or switch to the LWD collar, and see how the reading responds.
Borehole, rock and tool are drawn to scale. The front quarter of the rock is cut away and shown as a ghost so the gamma rays can be seen.