Marking Knives
A small incision in the timber with a marking knife is a much more precise mark to work to than a pencil line. Marking out in pencil first makes it easy to identify reference faces and edges and also gives you a chance to make changes before committing to a knife or scalpel line.
Because a marking knife line has depth, it can be used to register the tip of a chisel for the final paring cut, or bisected with a plane shaving to achieve very tight dimensional accuracy.