The frequency is taken from information found in the piece or supplied by the publisher or from evidence of issues already published. If there is no stated frequency, give the probable frequency when there is sufficient evidence to indicate the publishing pattern. Do not use a question mark. If the frequency is unknown, omit field 310 and code the fixed field bytes as "u/u".

Sometimes the stated frequency requires further explanation to account for irregularities in the publishing pattern. Such information is generally taken from the piece but may also be supplied and is given in parentheses following the frequency. Example:

When cataloging with a run of a serial in hand, you may find that the actual publishing pattern varies considerably from the stated frequency. In general, give the states frequency. In cases where it is obvious that the stated frequency is not the actual frequency, as evidenced by a number of issues and the numbering of those issues, give the actual frequency when it can be determined. Example:

See also:

13.3. Frequency notes (fields 310/321)