You'll have to describe a little better what the fields represent, how did you arrive at a sort number, etc. What exactly are you trying to do, besides sort by date? If you just want the records listed starting with 1, you could use Get(RecordNumber), but you wouldn't be able to sort by that number.
An unstored calculation can so this for small sets of records if you will keep the records in this sorted order. For larger record sets or for holding rank even with the records sorted differently, you could use Replace Field Contents with the same expression to assign the value to a number field:
Let ( R = Get ( RecordNumber ) ;
Case ( R = 1 ; 1 ;
GetNthRecord ( DateField ; R -1 ) = DateField ; GetNthRecord ( RankField ; R - 1 ) ; // copy same rank as previous
GetNthRecord ( RankField ; R - 1 ) + 1 // assign rank of previous record's rank + 1
) // Case
) // Let