How does multistrike work?

I'm having a hard time understanding Multistrike, and how it works compared to the tooltip.

So say I have 6 APS in my PoB, and I add a Multistrike to my gem setup, should I not have 18 APS now?
Or is there some other mechanic at play here that I don't understand?
I know the gem gives APS, so just disregard that aspect for now.

Since in my head, it's original hit + 2 more, per attack.
And since you are doing 6 attacks, that means 6x3=18.

I am extremely confused by this :P. So I am hoping someone can shed some light on this! <3

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Seffers wrote:

Since in my head, it's original hit + 2 more, per attack.
And since you are doing 6 attacks, that means 6x3=18.

Additional attacks don't happen simultaneously with you initial attack, they still take time. Gem gives you a lot more attack speed so they happen a lot faster than if you were to attack without it. And it still gives good amount of more damage for repeated attacks like other supports + additional attacks don't require mana to help with sustain