On display were some examples of Rockwell's studies for his Saturday Evening Post cover art. His studies were extremely detailed, little different from the final art apart from being drawn in pencil and lacking color.
Although this was highly labor-intensive, Rockwell in later years had an assistant to do some chores such as transferring a drawing to canvas, taking care of oil paints, cleanup, and such.
Below are some iPhone photos I took. Click on them to enlarge.
These are sketches of details and not a full-scale study.
Study for one of his most famous Post covers. Note the size compared to the nearby information plaque.
This compared the study with the final art. Most of the background details differ, so it's likely that a later study was made.
This is highly detailed indeed. Note that Rockwell paid attention here to light-dark values using other media then pencil.