The bracket themselves don't not make the difference in this PID in particular,
the whole equation is wrong.
Also notice how the wrong_load pid needed to be spelled
under description in the calc_pid.txt to be proper in the description row in the PIDs tab.
That is another issue tho.
P.S.
The PIDs here calc_pids(delta_load).txt show the current frame#,
and the difference in TPS% from the previous frame to the next.
Example:
frame #1 TPS% is 10%, frame #2 TPS% is 50%
delta_load will be 40%
Values will be negative with TPS% decreasing.
I use this both for filtering, enjoy.