This is my formula for adding up numbers in a column.

=SUM(IF(ISERR(FIND("-",J20:J137)),,REPLACE(J20:J137,1,FIND("-",J20:J137),"")-LEFT(J20:J137,FIND("-",J20:J137)-1)+1))

I have extended the length of the column to J20 to J183 as I now have more
entries, if I my manually change the J137 to J183 then the formula no longer
works.
Why is this? I dont understand the formula as it was done for me.

What am I doing wrong.

thanks