I just continued with Warframe after a week, I've almost got level 30 on my Excalibur and now I wish I didn't make the Scindo, but since I'm stuck with it for a while, what mods should I be putting on it?

I always believe mods should vary depending on who you're up against. I switch out an electric mod, fire mod, and armor pen mod depending on whether I'm against the corpus, infected, or grineer respectfully. Until I get more mod slots, then dual/triple/quad stacking elements because everything is better in pairs/triplets/quadruplets.

I tend to aim for a specific thing with each weapon, after all they're generally rigged to be better for certain things. A weapon with a bonus against infested should be given fire and used for infested missions, something with armour ignore is useful against grineer & corpus so best rigged for them.

Makes it easier building if you know what you want to build it for etc.

Dual ethers ignores armor, right?

Yes, they totally shred the grineer.

Oh I see, well. I have an electric mod for my Kraken and a have a 75% fire and rifle damage mod for my latron. Although I'm wondering wherever I should keep the latron or ditch it for a high rate of fire weapon since my kraken is fairly accurate.
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And I know this sounds stupid, but I don't know how to do the math to calculate how the Critical Chance mod will affect the base critical chance of a weapon.. :S

Ditch a Latron? HERESY! You could get mods to increase the fire rate.
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Critical chance mods are a % of it's base critical chance.

So a 7.5% weapon + a 10% mod (10% of 7.5) would result with an 8.25% change of a critical.

That's why it's not worth using crit mods unless the weapon has a high base crit chance.

In far more important news today is Friday, Rebecca said U8 was Friday. Yay.
*EDIT*

Daaaw, no U8 yet, few days extra. New frame instead today.

Oh. I didn't know that, I haven't come across a rifle fire rate increase mod yet.
And thanks! I finally get it xD
Wow. so that 40% crit chance with the krakens 2.5% base only gives me...
3.5% crit chance.... WELL. Getting rid of that garbage.

Time to start playing Warframe seriously again ^^

Been doing lots of wiki reading to try understand it, I never knew about how polarities affected fusion :o

Knowing how to fuse effectively is key in getting your shit to win levels. Same goes for knowing which mods are worth using with each weapon/frame.

I see, I'll refer to the Wiki for base stats of a weapon, but I don't think I can afford to make a Infected Weapon set and a Grineer Weapon set xP But that would be so cool..

Also, I saw the stalker on youtube, that guy is relentless