Autofill

[WIll]

I have this formula

=if(countif(b1:b2500, b1)>1, "duplicate","")

I want to autofill it all the way down the column, but the
computer keeps altering the range, when all i want it to
do is to alter the reference (b1). How do I make it do
that? example:

=if(countif(b1:b2500, b1)>1, "duplicate","")
=if(countif(b1:b2500, b2)>1, "duplicate","")
=if(countif(b1:b2500, b3)>1, "duplicate","")
=if(countif(b1:b2500, b4)>1, "duplicate","")

instead of:

=if(countif(b1:b2500, b1)>1, "duplicate","")
=if(countif(b2:b2502, b2)>1, "duplicate","")
=if(countif(b3:b2503, b3)>1, "duplicate","")
=if(countif(b4:b2504, b4)>1, "duplicate","")

 

[Peo Sjoblom]

Select the b:b2500 in the formula and press F4 or manually insert
dollar signs

=if(countif($b$1:$b$2500, b1)>1, "duplicate","")