To do a 'line3=line2-1 , check out the above() and below() functions to grab values from preceding or succeeding lines within the straight table chart.
from the help:
above([ total ] expression [ , offset [,n ]])
Returns the value of expression evaluated with the chart's dimension values as they appear on the row above the current row within a column segment in a table or, in the case of bitmap charts, in the chart's straight table equivalent (Actually all QlikView charts have a straight table equivalent with the exception of the pivot table which has a more complex structure.).
On the first row of a column segment a NULL value will be returned, as there is no row above this one.
If the chart is one-dimensional or if the expression is preceded by the total qualifier, the current column segment is always equal to the entire column.
If the table or table equivalent has multiple vertical dimensions, the current column segment will include only rows with the same values as the current row in all dimension columns except for the column showing the last dimension in the inter field sort order. The inter field sort order for pivot tables is defined simply by the order of the dimensions from left to right. For other chart types this can be manipulated in the Chart Properties: Sort dialog.
Specifying an offset greater than 1 lets you move the evaluation of expression to rows further up the current row. A negative offset number will actually make the above function equivalent to a below function with the corresponding positive offset number. Specifying an offset of 0 will evaluate the expression on the current row. Recursive calls will return NULL.
By specifying a third parameter n greater than 1, the function will return not one but a range of n values, one for each of n table rows counting upwards from the original cell. In this form, the function can be used as an argument to any of the special Chart Range Functions.
...Or if that doesn't help i suggest uploading a QVW sample that helps detail your need
