So if I understand you correctly you want to plot one indepedent and 2
dependent variables? Then your data will be every 3 rows? If so, adapt
the previous formulae as follows:

In C2:
=OFFSET($B$1, 3*(ROW()-ROW($C$2)), 0)
In D2:
=OFFSET($B$1, 3*(ROW()-ROW($C$2))+1, 0)
In E2:
=OFFSET($B$1, 3*(ROW()-ROW($C$2))+2, 0)

Does this help?
Kostis Vezerides