One of the most prevalent problems we encounter with author files is the incorrect uses of roman and italic characters. As a rule, all math variables should be typed as italic characters in the file. Roman functions should be set in roman font. Units of measure should be roman also. All too often, a file has been found to be unusable for production of author proofs because of the number of fonts changes that would have to be made to the file by the keyboarder.
For example, if an author typesets math variables as roman characters throughout a file, it means that a keyboarder must go through the file and change each character by hand, one by one. At this point, then, it is much easier to typeset the article from scratch, and we may have to reject your file.
Conversely, some authors will typeset units of measure or abbreviations for elements in italic fonts. This time, the keyboarder would have to change all the italics to roman fonts, and once again, the file would have to be rejected.
Here is an example of a chronic problem. The author has typeset the elements as italics:
The above should be typeset as shown below:
Another example: ``20 
'' is wrong. ``20 
m'' is correct.
Most math variables (with very few exceptions) must be typeset as italic characters.
Very often, authors will set roman functions as italic; these must
all be changed to roman. Use \sin, \cos, \tan, etc.,
not $sin$, $cos$, $tan$, etc.