Thread:Vae Victis/@comment-3400522-20130605203240/@comment-1264592-20130606085348

Lets try this in plain English, it helps me think straight before I get entangled with mathematics:

When you calculate the cost of getting an item you need to know how much you pay for all the failed attempts and how much you pay for the first successful attempt that gives you the item. The cost of the failed attempts is the cost of the conversion action multiplied by the chance to fail. The chance to fail is 1 minus the chance of success. The total cost of conversion is the cost of failure plus the cost of the successful conversion action.

Therefore, the cost to get a Sense of Deja Vu is: (1-success%)*(cost of a Tale of Terror!!) + (cost of a Tale of Terror!!). Which is (1-0.7205)*0.5+0.5 = 0.63975 Echos.

The cumulative cost is calculated in the way. For instance, when planning to create a Glimpse of Something Larger you need to take account of failure at the Tale of Terror!! level and the Deja Vu level. This means you need to add the cost of a single Sense of Deja Vu (which, as shown above, already includes the cost of failure) and a single Vision of The Surface to the chance of a failed conversion of a Deja Vu (again, its 1 minus the chance to succeed at that specific action - NOT the cumulative success rate!) multiplied by the cost of the Deja Vu and Vision of the Surface:

(1-success% of A Sense Of Deja Vu)*(cost of A Sense Of Deja Vu + cost of A Vision Of The Surface) + (cost of A Sense Of Deja Vu + cost of A Vision Of The Surface).

Which is (1-0.7178)*(0.63975+0.5)+(0.63975+0.5) = 1.461387 Echos.

The general formula is: (the cost of the previous step + the cost of the additional item) + [(1-success% of this step)*(the cost of the previous step + the cost of the additional item)]

Please tell if this logic makes any sense.