Since metric is a very general term, we recommend that authors adopt the International System of Units (SI) as the accepted metric system and terminology to be used. A basic reference for suggested usage is The International System of Units (SI), July, 1974, National Bureau of Standards, Special Publication 330, available in PDF format from the National Institute of Standards and Technology. See also Cassell's Dictionary of Weights and Measures.

Always consult your editor about the use of metric units in your book before you begin preparation of the manuscript.

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Uniformity in Numbering Various Elements
Use Arabic numerals for chapters and sections, tables, equations, figures, and appendices. We recommend the compound system (using a hyphen, not a decimal point) for numbering sections, equations, tables, and figures. Begin numbering each element anew at the start of every chapter. In this system the first number represents the chapter number; for example, the first equation in Chapter 1 will be (1-1), the first equation in Chapter 2, (2-1), and so forth. Enclose equation numbers in parentheses throughout-the only element so treated.

Capitalization, Spelling, Hyphenation
Capitalize and abbreviate the following elements when they are accompanied by numbers:

Fig. 5-2 Chap. 5 Eq. (5-1) Sec. 5-2 Prob. 6-8

Never abbreviate these or any other terms at the beginning of a sentence; spell out the word in such instances. Avoid using page numbers for references to these elements; instead refer to a specific table, equation, or section. Many word processors and page makeup programs can automate this numbering process; take advantage of the feature if you can. The use of page numbers delays return of page proofs to the compositor until missing references can be supplied. Check all cross references carefully before submitting your manuscript to be sure the numbering is correct.

Webster's New World Dictionary is our authority for spelling, hyphenation, and capitalization. Where two spellings are given for a word, use the first form shown.

Terms consisting of a capital letter and a noun are hyphenated only when they are used as attributive adjectives: for example, "I beam" but "I-beam structure"; "X ray" but "X-ray tube." Fractions are hyphenated: "a two-thirds balance," "two-thirds of those present." Do not use a hyphen in compounds containing an adverb ending in ly, such as "evenly spaced intervals."

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All letter symbols (with the exceptions noted here) used in mathematical equations or used to designate angles, curves, coordinate points, and so forth, are set in italics. Do not underscore letter symbols for italics. Our copy editors will do this throughout your manuscript for any you have missed.

Note that in italic context, letter symbols are also set in italics, but all numerals and all abbreviations are set in roman (ie, "Solve the equation for 2x - 2y.").

All abbreviations of chemical elements and compounds are set in roman.

Boldface
Each time they appear in your electronic files, apply bold to words, letter symbols, or other characters such as Greek letters or script that must be set in boldface. Do this with care; a copy editor cannot be expected to differentiate between boldface and lightface instances of the same character.

Do not indiscriminately apply bold or use boldface underscoring for an entire equation.

A - B - cos C - X^1-C-2X^1-C

When you are emphasizing the importance of an equation, bold only letter symbols, numerals, words, and abbreviations. Set operation signs and superscripts and subscripts lightface (unless the superscripts or subscripts contain a character such as a vector letter that must be set boldface).

A - B - cos C - X^1-C-2X^1/C

Where vector dots or cross products appear, set bold "times" signs as well as the vector letters.

Z - Y • dz - Y - Z x dy

If boldface roman and boldface italic symbols must be used, set them in your electronic file.

Boldface roman: X, Y, z

Boldface italic: X, Y, z

Wherever a center dot is used to indicate multiplication, center it; do not put it in the decimal-point position.

X • 2X • 3x    not    X _• 2X _• 3x

Monospace Fonts
Monospace fonts, such as Courier, give each letter and space the same width, just like a typewriter. Use a monospace font for setting computer statements, where alignment of characters is essential.

Identification of Symbols
Greek
Avoid hand writing Greek characters (or any other characters for that matter) on printouts of electronic manuscripts. Instead, set them in your electronic files. It is difficult to distinguish between many handwritten Greek characters and similar English letter symbols. The list in the next section identifies each of the Greek characters. Thus, the first time a lower-case handwritten alpha appears in your manuscript you should identify it in the margin as "lower-case Greek alpha." Note in the list of characters that some Greek letters have two lower-case forms. Also note the similarity between the capital psi, Y, and the lower-case form (unless you indicate otherwise, we shall assume the lower-case form of psi is meant).

Boldface Greek
Set boldface Greek characters as necessary in text files. A boldface Greek alphabet is shown in the next section. Notice that the boldface form varies from the lightface form.

Accented Characters
Characters common to technical composition, such as overbarred characters, are available as "one piece" in some typefaces; that is, the accent is cast on the same type body as the letter itself. Less common accents must be inserted over or under the letters. This involves tedious hand work. If in your files you are using a combination of characters to simulate an accented character not available in your font, you must provide a separate key to those symbols so the correct characters can be substituted globally.

Special Characters
If you must use a special character that has not appeared earlier in your manuscript, identify it the first time you use it. If we cannot find just what you want among the innumerable special characters that have already been made, it may be necessary for us to have the matrix for the character made to order, or we may ask for a substitute.

Spacing
Type operation signs, such as +, -, x, <, ³ with the equivalent of a single space on each side. However, type or write negative or positive quantities or terms "tight": ". . . as indicated by -x or +2." To indicate function notation or coordinate points or to separate two or more characters by punctuation, allow a single space after the punctuation:

the point (-4, 2)

or the case of f(x1, x2)

if we have D(a, b, c, ..., n)

Use a single space before and after all abbreviations:

6 H2C, 9 ft 6 in., 16 amu

Use a single space before and after integration and summation and capital pi signs. Type limits tight at the immediate right of integration signs and above and below summation and capital pi signs:

Use a single space before and after all differential terms, whether they are adjacent to other letter symbols or numerals, before or after parentheses or other enclosing signs, or before or after fractions:

However, when differentials appear as limits or as superscripts or subscripts, type them tight.

Matrices
Type matrices with three spaces between columns. If the terms in any column contain a varying number of characters, center the items in the column on the widest member of the column. If operation signs appear with any of the terms, use one space on each side of the signs unless negative quantities are involved; in such cases type them tight. In an electronic manuscript, use the table editor to create properly-aligned matrices.

When we typemark columns of matrices, we normally use a space equal to the width of the capital M in the type size being used (-em space) to separate the columns. If any symbols precede or follow the matrix, center them on the overall depth of the matrix. Include the punctuation that follows the matrix if you have used punctuation for centered matter.

Short Equations
If you consider two or more adjacent short equations important enough to center, place them side by side and space them well apart. Set off all but the last equation in each row with commas:

Whether equations are short or long, if they must appear one below the other, double-space them.

Superscripts and Subscripts
Where both superscripts and subscripts appear next to the same symbol, align them one above the other, unless you prefer that they be placed out of alignment; in such a case the superscript always follows the subscript-except prime marks, which precede the subscript.

Exponential e and "exp"
The use of e is feasible if the argument of the exponential is short or uncomplicated; if the argument is extensive or complex, the abbreviation "exp" is the better choice. In particular, we suggest the use of "exp" wherever more than one line appears in the argument, for example, where a superscript to a superscript or a "built-up" fraction (a fraction other than a simple numerical one) is used. Here are a few examples:

Punctuation of Centered Equations and Formulas
We suggest that no punctuation be used after centered equations or formulas. However, if you feel that such punctuation is necessary, use it consistently, considering each equation or formula in its context, as illustrated in the following examples:

The following equation indicates that we have arrived at a solution:

X2-Y2+1=24c,

where both X and Y are constant. We can find our solution by writing

X - Y + 1 = 0.

Three possibilities exist in this instance: X + 1 = c, X+ 2 = c, or X + 3 = c.

In the last example note that short equations are placed side by side on the same line to conserve space and that a comma is used after all but the last equation. If you were omitting terminal punctuation, you would still use the commas after all but the last in a series of short equations on the same line.

Fractions: Solidus vs. Built-up
Use the solidus (diagonal rule) fraction in text matter unless the fraction is complex. Signs enclosing individual terms will prevent ambiguity in many complex fractions and thus permit use of the solidus. Avoid built-up fractions in the text, since they require the compositor's insertion of spacing material above and below the line in which they appear in order to support the built-up structure. Space between the lines detracts from the readability and appearance of the material. By converting built-up fractions to solidus fractions, we eliminate the problem. Note the ungainly appearance of built-up fractions in running text:

. . . in Eq. (2-1) we indicated that was not part of the required general solution,

which would have to involve .

The additional elimination of

, is a consideration.

Solidus fractions provide a more compact and attractive presentation:

. . . in Eq. (2-1) we indicated that x (dx/dy) was not part of the required general solution, which would have to involve x - y (dx/dy) - z1/2. The additional elimination of (dx/dy)(a2/b2) is a consideration.

In centered expressions we recommend use of the built-up fraction throughout; if you prefer the solidus fraction in centered matter, use enclosing signs in the conventional order of { [ ( ) ] } where necessary.

Abbreviations
Be discreet in your use of abbreviations-use only those that are accepted as standard in your field; even then, consider whether your reader will be familiar with them. Define any abbreviation that might be confusing if it were introduced without explanation. Here are a few specific rules for the abbreviation of physical units:

1. Abbreviate when the unit is used with a number, except at the beginning of a sentence:
   
   12 in. 4 V 2 oz 16 in-lb
   
   Twenty pounds of lead . . .
   
   
   
2. Use the singular form for the abbreviation of both singular and plural quantities:
   
   1 kg 1/2 f 1 cu yd 0.5 m
   
   20 kg 23 ft 100 cu yd 605.5 m
   
   
   
3. Spell out approximations:
   
   . . . about five centimeters.
   
   . . . a thickness of several inches.
   
   
   
4. In general, omit the period after abbreviations. But note that the abbreviations for atomic weight and inch are exceptions:
   
   50 mph 6 ml 22 amp 6 in.
   
   sin cos tan sec
   
   co mm at. wt. 12 ft-lb
   
   
   
5. Do not use signs such as ' for feet, " for inches, # for number, or X for "by" between dimensions, except in drawings, specifications, or tables:
   
   12 ft not 12'
   
   12 by 12 in not 12" X 12"
   
   An exception is the use of the percent sign (%) in running text or centered equations if its appearance is frequent in the manuscript, provided it is preceded by a number or symbolic notation: 12 % H20, Y %.
   
   
   
6. Abbreviate figure, chapter, and equation if these are followed by numbers or letters; do not abbreviate them if they begin a sentence:

   Fig. 5-2 Chap. 5 Eqs. (5-1) and (5-2)
   
   . . . in the first equation. Figure 5-2 shows how . . .

Compound Abbreviations
If your text contains many references to compound units, the abbreviation of units without numerical values is recommended. When you refer to compound units, be consistent in the use of either the solidus or "per." Any of the following ways of showing compound units is satisfactory as long as the same form is used throughout:

. . . is measured in cubic inches per foot per degree Kelvin.

. . . is measured in cu in. per ft per K.

. . . is measured in cu in./ft/K.

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The capital and lower-case forms of the Greek alphabet are shown in the following table; the letters at the left in each column are capitals:



Boldface Greek
In the example below, we have omitted those letters that are similar to English forms. Boldface Greek is different in appearance from lightface Greek.

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