It may be of any length, but at one end it should be filed so as to leave a Scribing point that will come close to the base circle or line, and have a short handle, as shown in Fig.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
The work is set true to the lines by a Scribing block, or surface gauge, but as that instrument is more used in setting work with chuck dogs its application will be shown in connection with chucking by dogs; hence to proceed: To set the work true to the line A it may be necessary to place a thickness of paper, a piece of sheet tin, or the equivalent, beneath one of the parallel pieces to bring A parallel with the chuck plate surface.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose
2430; A being the iron plate and B the square; and, supposing the box to be true, as it usually is, we may set a Scribing-block, as shown in Fig.
"Modern Machine-Shop Practice, Volumes I and II"
Joshua Rose