(2) With the centre B (the compass leg being in all cases placed with absolute accuracy, using a lens if necessary to place it) describe the circle C D E.
(3) With the centres C and E, and with a radius of not less than 9 inches, describe arcs intersecting at F and G.
(4) Join F G.
Then, if the work has been correctly done, the line F G will pass through the point B, and be perpendicular to the line A B. If it does not do so, the work is incorrect, and must be repeated.
When the base and the springing-line are drawn on the form, the form must be accurately measured from the bottom upwards, and every foot marked on both sides.
Such markings to be in fine pencil-line, and to be drawn from the sides of the form to the extreme margin of the paper, and you are not to trust your eye by laying the lath flat down and ticking off opposite the inch-marks, but you are to stand the lath on its edge, so that the inch-marks actually meet the paper, and then tick opposite to them.
Also if there are any bars in the window to be observed, the places of these must be marked, and it must be made quite clear whether the mark is the middle of the bar or its edge; and all this marking must be done lightly, but very carefully, with a needle-pointed pencil.
In every case where the forms are set out from templates, the accuracy of the templates must be verified, and in the event of the base not being at right angles with the side, a true horizontal must be made from the corner which is higher than the other (the one therefore which has the obtuse angle) and marked within the untrue line; and all measurements, whether of feet, bars, or squaring-out lines, or levels for canopies, bases, or any other divisions of the light, must be
made upwards from this true level line."
These rules, I suppose, have saved me on an average an hour a day since they were drawn up; and, mark you, an hour of waste and an hour of worry a day—which is as good as saving a day's work at the least.