According to Cataloging Cultural Objects: A Guide to Describing Cultural Works and Their Images, the creation date of an artifact is made up of three components: a free-text field, which is indexed using “two numbers to delimit the beginning and end of the implied date span.” In TMS, this information is recorded in the Objects.Dated, Objects.DateBegin, and Objects.DateEnd fields respectively. TMS can accurately determine the beginning and end years of the span, when the date consist of a single year, a span of years, or when the ambiguity of the year is implied with “circa,” but when the creation date is expressed by the nearest decade or century, you will need to enter the search dates manually.

The beginning and end years for centuries are often erroneously calculated (see: The Battle of the Centuries, by Ruth Freitag).

The n-th century CE will have a beginning year of 100n – 99, and will have an ending year of 100n. In TMS these are expressed as positive integers.

The n-th century BCE will have a beginning year of -100n, and will have an ending year of -100n + 99. In TMS these are expressed as negative integers.

Most conventions will allow for the division of decades or centuries into quarters, thirds (early, middle, late), or halves. In this case the following formulae can help you to determine the beginning and ending years.

The formulae use five variables:
b = the beginning year of the date span (decade, century, millennium)
t = the quantity of years within the date span prior to dividing it (ten, hundred, thousand, respectively)
s = the quantity of segments to divide the date span into (four for quarters, three for early/middle/late, 2 for halves)
q = the quantity of segments desired
z = 1 for years CE or -1 for years BCE

Beginning year = b + z((t ÷ s) × (q – 1))

Ending year = (b – z) + z((t ÷ s) × q)

Round to the nearest integer, when necessary.

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