Hi, What do you think a "4 layer black box" is exactly in the following sentence: "Your keyboard should be in the middle of your desk and your phone either on the right or left hand side, along with the ‘aide-mémoire’ and 4 layer black box to put in all of your personal working material" Une boîte à 4 étages ? Un bloc tiroir ?? Une étagère à 4 niveaux ??? Thank you for your help !