date at

date at is used to determine the date of a particular sample.

For example, given the following case fragment,

           01 Jun 03    20 Jun 03    03 Sep 03    15 Oct 03    02 Nov 03
ABC           2.5          2.3          2.2          2.1          2.0
DEF           6.3                       4.0          1.9

date at most recent DEF is “15/Oct/03”

date at first ABC is “01/Jun/03”

date at max DEF contains “Jun”