Draggin ranges

[ExcelMonkey]

I have a sum formula in cell R1 that basicall says:

=A1+B1+C1

I want to be able to drag cell R1 to S1 and have the formula say:

=D1+E1+F1

However when I drag it it automatically says:

=B1+C1+D1

Is there anyway to drap the cell such that it nows how to update to :

=D1+E1+F1

Thank

 

[Frank Kabel]

Hi
enter the following in R1
=SUM(OFFSET($A$1:$C$1,0,(COLUM()-COLUMN($R$1))*3))
and copy this to the right