UDC Summary/Consecutive extension (oblique stroke sign). Table 1aThe extension sign / (stroke or slash) connects the first and last of a series of consecutive UDC numbers to denote a broad subject, or range of conceptsIf the number following the stroke is more than three digits long and begins with a group of digits in common with the preceding number, it may be abbreviated by omitting the digits common to both, so long as the first item after the stroke is a point. Thus, in the notation built from 629.734 and 629.735, the group 629 is common to both and is not repeated; the group .735 following the stroke is coordinate with .734 preceding it: 629.734/.735; this is equivalent to 629.734+629.735