Pencil: If you sharpen it regularly with a pencil
sharpener, an ordinary pencil will do.
Rule: An 18"(500mm)-long stainless steel rule
is sufficient. The metric rule must have 0.5mm marks and the
imperial rule must have 1/64" marks over the entire length. If
you want a high-quality rule, get a Starrett one.
Square: Buy a quality steel
square.
Caliper: A quality caliper should
be in every guitarbuilder's toolbox.
Thickness gauge: I use a Japanese-style thickness
gauge. The excellent Veritas gauge is shown on the right.