How are speed modifiers calculated?

Production Line Game discussion
1

There are three options to add additional robots to a slot. How are these 3 modifiers calculated?

Are they added to a total of +17,5% or is there another system? I tried to figure this out myself, but it seems like a really strange system to me.

Any help would be really appreciated.

2

Each additional robot will reduce the time taken by a slot to reduce the time for production.

Example:

The tier 1 Chassis Assemble slot will take 12m58s to complete a single run.
With a second par of robots it comes down to 11m42s.
A third set of robots brings production run time down to 10m57s and finally the fourth set of robots bring the production run time on that slot down to 10m30s

3

That’s not what I meant. I can read tooltips.

What I meant is how exactly are the modifiers calculated? Because to me this system seems really strange.
I already put some numbers into excel and they don’t make any sense:

1401×431 25.7 KB

So if anyone knows how this is possible please tell me.