Hi Taha,

If you insert into cells A1 through D24:

10-Jan-2005 0.000
11-Jan-2005 XXX 1 6
12-Jan-2005 XXX 1 6
13-Jan-2005 XXX 1 6
14-Jan-2005 XXX 1 6
15-Jan-2005 5.000
16-Jan-2005 XXX 6 24
....
02-Feb-2005 -13.000

and replace XXX by
=OFFSET($B$1,C2-1,0)+(OFFSET($B$1,D2-1,0)-OFFSET($B$1,C2-
1,0))*(A2-OFFSET($A$1,C2-1,0))/(OFFSET($A$1,D2-1,0)-OFFSET
($A$1,C2-1,0))

in cell B2 and copy it onto the other XXX cells, this
should work fine. Hint: Values in columns C and D tell the
formula where to look for given values (row number).

HTH,
Bernd