Arrays

[Tom]

If you change only one of the references to the variable the behavior will be different.

When you store the sum of DURATION and something else back into the variable DURATION then you see that you are using it as an accumulator (like the Memory + key on your calculator).  But if instead you store the sum of DURATION and something into a different variable (TIME) then it is no longer accumulating.  If there is not some other statement somewhere to add values to the DURATION variable it will always be missing.  So

Time = sum(duration, ext{i} - itb{i}) becomes the same as Time = ext{i} - itb{i} since the variable DURATION is not contributing anything to the SUM().