If you look at the help for peek(), you'll read that 0 denotes the first record. So you need to start your loop at zero.
Returns the contents of the fieldname in the record specified by row in the internal table tablename. Data are fetched from the associative QlikView database.
Fieldname must be given as a string (e.g. a quoted literal).
Row must be an integer. 0 denotes the first record, 1 the second and so on. Negative numbers indicate order from the end of the table. -1 denotes the last record read.
If no row is stated, -1 is assumed.
Tablename is a table label, see Table Labels, without the ending colon. If no tablename is stated, the current table is assumed. If used outside the load statement or referring to another table, the tablename must be included.
peek( 'Sales' )
returns the value of Sales in the previous record read ( equivalent to previous(Sales) ).
peek( 'Sales', 2 )
returns the value of Sales from the third record read from the current internal table.
peek( 'Sales', -2 )
returns the value of Sales from the second last record read into the current internal table.
peek( 'Sales', 0, 'Tab1' )
returns the value of Sales from the first record read into the input table labeled Tab1.
Load A, B, numsum( B, peek( 'Bsum' ) ) as Bsum...;
creates an accumulation of B in Bsum.