Need Help with SSUM

I need some help with the SSUM instruction for logix.

This instruction has IN1 and IN2 being used as well as Select1 and select 1 and out.

The enable bit is 1 and is just placed inthe instruction not a tag so it is on all the time. In 1 is line speed and In2 is slack takeup speed. Select 1 is 1 and is placed in the instruction and not by a tag. Select 2 is a bool tag from a pushutton 1 or 0.

My understanding of the instruction help is that if select 1 and 2 are both off i will have no output correct. Well select 1 is always on which is line speed when i hold the pb and select 2 is high does it add/ sum slack tke up speed value and line speed and just outputs line speed when the PB is low 0?

Is my understanding correct.

The instruction help is a little vague.

Uhh, yes?
It sums together any input that has the corresponding 'select' bit set.

If a select isn't set, the contribution of that input is 0.