The perfect site tool is a compact oil filled cartographic compass with fast north needle on a sapphire bearing and neck cord.
A good value compass when it comes to map reading and taking directions for sites and monuments, or positioning your north arrow. The transparent yellow/green body makes it difficult to lose.
In general this adds up to a good all round site compass.

Rules: mm, cm, 1/8 inch
Graduations: 2º, 10º, 20º