To hold the centerline on the workpiece will help the device shown in the figure.
Recommend to read
IMPROVED PROBE
Primitive "control print" — electroputere with two wires and the lamp — not the best device for "continuity" of electric circuits. Commercially available testers and isometry is also...
ECONOMICAL PENCIL
When the hand is not a pencil of suitable color or hardness. would be useful and "bits", but they are inconvenient to use, they can be extended by sticking in a metal or plastic tube of...
