It sometimes happens through the unskilfulness of the _Joyner_, (for they commonly, but unproperly, imploy _Joyners_ to make them) that a Length shall be hollow in the middle both on the Face and Foot, and shall run driving higher and higher towards both ends: Hence it comes to pass, that when the _Compositer_ cuts a piece of _Rule_ to his intended Length, the _Rule_ shall _Print_ hard at one end, and the other shall not _Print_ at all; So that he shall be forced to knock up the foot of the low end, as shall be shewn in its proper place. But the careful _Master-Printer_ having found that his _Brass-Rules_ is _Letter_ high all the whole Length, will also examine whether it be straight all the whole Length, which he does by applying both the Face and Foot to the surface of the _Correcting-stone_; And if the Face and Foot comply so closely with the _Correcting-stone_, that light cannot be seen between them, he concludes the _Brass-Rule_ is straight. [Illustration: _Plate 1._] Then he examines the Face or Edge of the _Rule_, whether it have an Edge of an equal breadth all the whole Length, and that the Edge be neither too thick nor too fine for his porpose. He should also take care that the _Brass_, before it be cut out, be well and skilfully Planish’t, nor would that charge be ill bestowd; for it would be saved out of the thickness of the _Brass_ that is commonly used: For the _Joyners_ being unskilful in Planishing, buy Neal’d thick _Brass_ that the _Rule_ may be strong enough, and so cut it into slips without Hammering, which makes the _Rule_ easily bow any way and stand so, and will never come to so good and smooth an Edge as Planish’t _Brass_ will. Besides, _Brass_ well Planish’t will be stiffer and stronger at half the thickness than unplanish’t _Brass_ will at the whole: As I shall further shew when I come to Exercise upon _Mathematical Instrument-making_. §. 3. _Of_ Cases. Next he provides _Cases_. A Pair of _Cases_ is an _Upper-Case_ and a _Lower-Case_. The _Upper-Case_ and the _Lower-Case_ are of an equal length, breadth and depth, _viz._ Two Foot nine Inches long, One Foot four Inches and an half broad, and about an Inch and a quarter deep, besides the bottom Board; But for small Bodied _Letters_ they are made somewhat shallower, and for great Bodies deeper. _Long-Primmer_ and downwards are accounted small Bodies; _English_ and upwards are accounted great Bodies. The conveniencies of a shallow _Case_ is, that the _Letters_ in each Box lye more visible to the last, as being less shadowed by the sides of the _Boxes_.