Classification of Standards:

1. Line & End Standards: In the Line standard, the length is the distance between the centers of engraved lines whereas in End standard, it is the distance between the end faces of the standard. Example: for Line standard is Measuring Scale, for End standard is Block gauge.

 Primary, Secondary, Tertiary & Working Standards:

Primary standard: It is only one material standard and is preserved under the most careful conditions and is used only for comparison with Secondary standard.

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Secondary standard: It is similar to Primary standard as nearly as possible and is distributed to a number of    places for safe custody and is used for occasional comparison with Tert iary standard.

Tertiary standard: It is used for reference purposes in laboratories and workshops and is used for comparison with working standard.

Working standard: It is used daily in laboratories and workshops.  Low grades of materials may be used.