I have a list of dates in a column, that is sorted by name and then date.  
The dates vary, but in assending order for each person.  I have also filtered
the data by determining which dates would be sequential, using a break of two
days - ie-weekend, as sequential periods.  I realize that for two dates, one
a monday and one a wednesday or thursday, this would assue a sequential
period, but I will then subtotal on a count to determine how many days are in
the sequential period to see if it is in agreement.  I am trying to write a
formula using a LET statement similar to

=if(F3=1,Return the value for Duration and then Let Duration=0,Duration+1),

Where Duration is a named range that I am trying to work as a counter to
determine duration and then rest to zero for each new name in a range.  I
used to use Let statements, but that may have been in my Lotus 123 days or
maybe Cobol.