Formula is changing after a date sort

edited 12/09/19 in Smartsheet Basics

Once my data is in the appropriate cells I want to perform a sort by Due Date.  When I do this

the formula

=SUMIF($Equipment5:$Equipment171, "VUTEK", $Tue5:$Tue171)

Changes to

=SUMIF($Equipment16:$Equipment171, "VUTEK", $Tue16:$Tue171)

Thus not including any data from rows 4 thru 15.

I have locked the row with the formulas but does not work.