Writing board set and peeking prevention system

A writing board set comprising:

• a writing board that includes
• a first polarizing layer having a transmission axis that is parallel to a first direction and
• a diffuse reflection layer or a diffuse reflection plate to diffuse-reflect visible light, the diffuse reflection layer or diffuse reflection plate being disposed on an opposite side of the first polarizing layer from a viewer's side;
• and
• a writing utensil containing ink, wherein,
• Ld*, ad*, and bd* are values of L*, a*, and b* as obtained by irradiating a surface of the writing board at the viewer's side with light that has been transmitted through a second polarizing layer having a transmission axis which is orthogonal to the first direction, and measuring total reflectance through spectrophotometry;
• Lc*, ac*, and bc* are values of L*, a*, and b* as obtained by introducing the ink onto the surface of the writing board at the viewer's side and irradiating the surface having the ink introduced thereon with light that has been transmitted through a second polarizing layer having a transmission axis which is orthogonal to the first direction, and measuring total reflectance through spectrophotometry;
• and
• a color difference ΔE*ab as defined by eq. (2) is 12 or less:
• ΔE*ab[(Lc*−Ld*)2+(ac*−ad*)2+(bc*−bd*)2]1/2 (2).