In works that are published in different sizes, this is the changing of the margin from the small paper to the large paper edition, when at press.
After the margin for the small paper copies is finally made, the additional width of the gutters, the backs, and the heads, is ascertained in the same manner, by folding a sheet of the large paper, that it was in the first instance. The additional pieces for the change should, if possible, be in one piece for each part. See Margin.
The alteration of margin requires care, for it occasionally happens that the sheet is imposed with the wrong furniture; and where it happens to be in one form only, and that form is first laid on, it sometimes passes undiscovered till a revise of the second form is pulled, when the error is detected, but too late to rectify it; the consequence must be, to cancel a part of the sheet, or to print the reiteration with the margin also wrong; nay, sometimes both forms are worked off with the furniture wrong, without being perceived till the compositor comes to distribute, particularly when they are printed at different presses. Such errors destroy the uniformity of the book, and spoil its appearance.
These mistakes can only be avoided by care and attention on the part of the compositor, the reader, and the pressman; but I would recommend that the furniture for the alteration should be cut of different lengths from the furniture of the small paper: in octavos the gutters and backs should be the exact length of the page, and be always imposed within the sidestick; and the head should be the width of the two pages and the gutter, and be imposed within the footstick. This method of cutting the furniture of precise lengths for the alteration, and locking it up within the side and foot sticks, will not only distinguish it from the rest of the furniture, and from the pieces that may be put in for the convenience of quoining the form, but will also preserve it from being injured by the mallet and shooting stick, in locking up, and by the indention of the quoins.
The same principle, of cutting the alteration to precise lengths, and locking it up within the side and foot sticks, will hold good in all other sizes, where it is required : in quartos, the pieces must be cut to the length and width of the page; and in folios to the length of the page only, as the margin of the head is regulated at the press.