If the data you want to SUM is in B2,B3 and B4. Then enter the following
array formula. Do not type the { } brackets when entering the formula.
After typing in the formula press the Ctr&Shift and Enter this will add
the { } and make it an array..
{=SUM(IF(ISERROR(B2:B4),"",B2:B4))}
Charlie O'Neill
