Character position definition and scope:

A one-character alphabetic code indicates the reduction ratio range of a microform.  The specific reduction ratio is recorded in 007/06-08 (Reduction ratio).

For microfilm created by other than COM (Computer-Output-Microfilm) processes and for microopaque microprints, codes a and b are most likely to be used.  For COM microfiche or microfilm, the reduction ratio is actually an expansion ratio and refers to the ratio of expansion required to produce a legible image.  Most COM is created at 024-048 reduction ratios (codes b and c), though some COM fiche is at higher ratios (e.g., 072).  Codes b-e are used with other types of microforms (e.g., microfiche, ultrafiche, etc.).  The most commonly encountered microfiche are normal reduction (code b).

The reduction ratio is usually given on the microform itself.  If it is not present, one must know the dimensions of the original item and the size of the image on the microform in order to code the information needed in 007/05.

A fill character ( | ) is used when no attempt has been made to code this position.

Record requirements for National-level and Minimal-level records:  Optional.

Guidelines for applying content designators:




Low reduction  Less than 16:1 ratio (less than 016).


Normal reduction  Between 16:1 and 30:1 (016-030).


High reduction  Between 31:1 and 60:1 (031-060).


Very high reduction  Between 61:1 and 90:1 (061-090).


Ultra high reduction  Over 90:1 (over 090).




Reduction rate varies


No attempt to code

Related MARC field or document:

07/06-08 Microform:  Reduction ratio

To return, select:

007:  Microform

007  Physical Description Fixed Field