Karnaugh-Veitch Ruler

These Karnaugh-Veitch table/diagram/map rulers are the solution to every digital/logic circuit engineers pain of drawing an extensive amount of KV-diagrams. They are designed to fit a standard 5mm rastered notepad and ballpens.

The modern version isn't very useful, however oddly unique -- for all the cool kids out there. The other, simple ruler is extremely practicable and perfect for everyday use. You can even spice this one up by omitting top and bottom solid layers and choosing a nice infill pattern.