What did Louis do to measure the cardboard box?

When Louis arrived at his apartment in Europe he found a note pinned to the wall in his study. The note was pinned on a 10 Euro bill. It was from his yankee roommate Jack, who always liked to play games.

The note said:

“*This 10 Euro bill is yours if you confirm for me that the dimensions of the empty box on the floor are 15Long X 11Wide X 15High in inches—yes inches!

The only thing you can use to measure the box is a flat wooden strip sitting next to the box, which is 35 inches long. Using anything in this room only, you can make only ONE mark on this flat wooden strip. There is a small pencil next to the strip. For measurements, you can only contact the strip and the box. Your measurement must be within +/- 0.05 inches.