Timestamp diff () in IDT

  Hello experts ,

I need to find difference in years between  the current  time stamp and  REF_DT time stamp . I  figured to use  now() function to get current time stamp .

The is the expression i tried to get the year

timestampDiff (6, REF_DT,now() ) 

I am not sure why  the numeric 6 in the first argument  . In fact i  am not sure  how to define 1st numeric argument .

Any help  on how to use timestamp Diff ()

usage timestamp DIff ( Expression : NUmeric ,First argument:Date Time , Second argument  DateTime)