3. All drawings must be made with the pen only. Every line and letter, signature included, must be absolutely black. This direction applies to all lines, however fine, to shading, and to lines representing cut surfaces in sectional views. All lines must be clean, sharp, and solid, and they must not be too fine or crowded. Surface shading, when used, should be open. Sectional shading should be made by oblique parallel lines about 1⁄20 of an inch apart. Solid black should not be used for sectional or surface shading.
4. Drawing must be made of the fewest lines possible, consistent with cleanness. The plane upon which a sectional view is taken should be indicated by a broken or dotted line. Heavy lines on the shade side of objects should be used, except where they tend to thicken the work and obscure letters of reference. The light is always supposed to come from the upper left hand corner at an angle of 45 degrees.
5. The scale to which a drawing is made should be large enough to show the mechanism without crowding. The number of sheets used must never be more than is absolutely necessary.
Fig. 292.
6. The different views should be consecutively numbered. Letters and figures of reference must be carefully formed. They should, if possible, measure at least one-eighth of an inch in height.
If the same part of an invention appears in more than one view of the drawing it must always be represented by the same character.
7. The signature of the inventor is to be placed in the lower right-hand corner of each sheet, and those of the witnesses at the lower left-hand corner.
The title should be written with pencil on the back of the sheet.
Drawings should be rolled for transmission, never folded.