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D.R.A.I.C.H. :: 8th Ed. :: Casting Probabilities 
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Lord of the Dragon Caves
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Ok -- I did an Excel spreadsheet that calculates the true percentage to cast spells using different numbers of power dice. The table takes into account the possibility of a successful casting due to irresistible force on a double 6 roll that is less than your target number (which the table linked to in another thread fails to consider). Also, the table goes up to target numbers up to 24 and considers use of up to 7 Power Dice.

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Mon Jun 28, 2010 12:39 am
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I assume the casting number is the number added to your wizard level needed to get the spell of?


It's a nice sheet, I'll add i to the 8th edition part in the D.R.A.I.C.H. for now

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Mon Jun 28, 2010 4:22 am
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Lord of the Dragon Caves
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Casting number is the target number you need to roll to cast the spell. For example, a level 4 (+4 to cast) casting the enhanced version of Purple Sun (casting value 25) would look at the column for 21 since that's the number that needs to show on the dice for the spell to go off.

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Mon Jun 28, 2010 4:31 am
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Ok then my thinking was right, it's a usefull chart to enhance my play as i always have some doubts about the number of dice to use. Thanks

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Mon Jun 28, 2010 11:21 am
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Hmmz it seems to me a good general rule is to divide the number you need to roll by 3, if you have sac dagger round down, if not round up, and that's the number of d6 you should roll for a reliable casting.

If there's no remainder and you don't have a dagger then its up to you whether you want to risk failure (max chance 33.3%) or roll another dice (and increase miscast odds).

Damn good chart :)


Tue Sep 21, 2010 1:00 pm
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This should be stickied me thinks.

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Sat Nov 06, 2010 8:50 pm
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Svarthofthi wrote:
This should be stickied me thinks.

Yup. I've printed it up to keep with me. Pretty great list for those of us not mathematically inclined. ;)


Sat Nov 06, 2010 10:31 pm
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Just noticed - as casting number goes up from 21->24 the % of casting with 4d6 goes up.

Regardless, this table has been incredibly useful to me, and hopefully more people will see it :)

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Sat Dec 29, 2012 1:05 am
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Lord of the Dragon Caves
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There was a mistake in my Excel spreadsheet that affected the calculation for higher casting values. Specifically it had to do with the the probability of an IF result that totals less than the target number. A correct calculation can be found in a more recent thread I am currently having trouble locating due to the fact I am on my phone not my computer ... Will find it later unless someone else beats me to it.

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Sun Jan 06, 2013 9:13 am
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Perhaps it was this thread?
http://www.druchii.net/viewtopic.php?t=71090

It got juggled into "other races" with the newly ordered forums. Perhaps we can move it to Druchii tactics?

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Sun Jan 06, 2013 10:40 am
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Lord of the Dragon Caves
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That's the one I'm thinking of. I might also edit the first post of this thread to reflect the corrected table further down your thread (giving you credit of course).

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Sun Jan 06, 2013 1:17 pm
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Ohh.. Sure, but in the end we both got there so it makes little difference :)
I was thinking of making a Druchii reference PDF cheat sheet with such probabilities on it. But perhaps we can condense your table a bit further? Or list some rules of thumb. For example: castvalue divided by 3 and rounded gives the number of dice for 80-ish percent success, but if you add 1 more dice that's 90-ish percent.

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Sun Jan 06, 2013 4:58 pm
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Lord of the Dragon Caves
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That's a good idea. Condense the table and put it on a cheat-sheet with other spell-related stuff, such as IF/miscast probability, the rule of thumb re: number of dice, and a summary of casting restrictions (like the one in the reference section of the rule book but corrected to reflect the errata). Maybe spell summaries of the lores available to Druchii (edited to avoid copyright issues). I could put together a PDF and host it. Anything else you think would be good to have?

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Sun Jan 06, 2013 5:33 pm
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Perhaps one could toss in odds for miscasts based on Ring of Hotek.. although.. I doubt that's really useful for a cheat sheet during battle (You want the ring close regardless).

I'd start at that, really. We can add to it as we go :)
I could host the PDF too, if needed. It's as you wish.

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"I move unseen. I hide in light and shadow. I move faster than a bird. No plate of armour ever stopped me. I strike recruits and veterans with equal ease. And all shiver at my coldest of whispers."
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Sun Jan 06, 2013 6:52 pm
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Rather than using a cheat sheet, I've been sticking to the following rule of thumb like glue (unless the powerdice and battle forced me to take more risks):

(1) Take cast value, deduce caster's level.
(2) Divide the remaining cast value by 3. This yields a number of powerdice for a good, but not excellent success chance.
(3) Add 1 more power dice for optimal odds.

Of all spells cast with the "optimal" number of powerdice, I have had 1 IF and 1 spell failures total over the course of 5-6 games. I've been forced to deviate from the optimal number of dice only a couple of times, which yielded me 1 cast failure and 1 IF as well, but over a considerably fewer amount of casting attempts.

So far this is proving a golden rule for me.

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Tue Feb 05, 2013 3:16 pm
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@Daeron:
Interesting idea, sounds like it would work like a, excuse the pun, charm. Couple of questions
1) Do you round up or down after dividing?
2) If you have the Sac dagger what do you do?

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Wed Feb 06, 2013 8:05 am
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Well.. I simply round it "the proper way": 13+ / 3 = 4.33333, rounds to 4 dice but it's risky. 5 dice is optimal. 14 / 3 gives 4.66667, rounds to 5 dice with a good shot at getting it but a 6th one will give it that extra insurance (Around 12% better).

Basically, if rounding makes the number go down, you're taking a risk by not adding a dice. If rounding makes the number go up, you're looking at a good shot, but you could improve it with 1 more dice if you plan to still cast other spells that phase.

To help your intuition value these numbers:
- 13 to cast: 13/3 = 4.333 = 4 dice, 66.4%. This is close to rolling a 3+ on 1 dice.
- 13 to cast, 4 dice + 1 for insurance gives 90.2% which is slightly better than a 3+ with a reroll on 1 dice.
- 14 to cast: 14/3 = 4.666 = 5 dice. 84.8%. This is close to rolling a 2+ on 1 dice.
- 14 to cast, 5 dice + 1 for insurance gives 96.4%, which is close to having a 2+ roll with a reroll on 1 dice.

I have not used any theorycrafted rules yet when wielding the dagger. Since you can choose the action halfway, statistics can get a little screwy. Thus far, my logic has been to use 1 dice up to 4+ casts (which on a level 4 means up to 8+) and 2 dice up to 7+ (11+ on a level 4).
I'll see if I can give that some thought.

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Wed Feb 06, 2013 9:55 am
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It proved an interesting exercise to work out the effect of the dagger. I started out by listing all possible types of behavior, did some thorough thinking, calculated some results and it yielded me the exact same result as casting the spell with 1 dice more.
I'm still working on a way to double check my outcomes but that's essentially what it comes down to.

Assuming you will use a sacrificial dagger in any of the following situations:
- You missed the cast value by 6 or less.
- You missed the cast value by more than 6, but you rolled 1 six, and hope for an irresistable force.
In these cases, your odds are identical as if you would throw an extra powerdice. So literally, the sacrificial dagger permits you use one powerdice less without loosing any reliability in your casting.

The exercise proved more valuable because the intermediate work made it easy to calculate a different strategy, where you will use the dagger only if it's fairly "safe":
- You misssed the cast value by less than 6 (there's risk on IF, but there's a chance of getting spell without IF still)
OR
- You missed the cast value by 6 but didn't roll any other 6, so there's no risk on IF.

In this case, we get slightly different numbers:
Value . . 1d6 . . . . . 2d6 . . . . . 3d6 . . . . . 4d6 . . . . . 5d6 . . . . . 6d6
03+ . . 97,22% . . 100,0% . . 100,0% . . 100,0% . . 100,0% . . 100,0%
04+ . . 91,67% . . 99,54% . . 100,0% . . 100,0% . . 100,0% . . 100,0%
05+ . . 83,33% . . 98,15% . . 99,92% . . 100,0% . . 100,0% . . 100,0%
06+ . . 72,22% . . 95,37% . . 99,61% . . 99,99% . . 100,0% . . 100,0%
07+ . . 58,33% . . 90,74% . . 98,84% . . 99,92% . . 100,0% . . 100,0%
08+ . . 41,67% . . 83,80% . . 97,30% . . 99,73% . . 99,98% . . 100,0%
09+ . . 27,78% . . 74,07% . . 94,60% . . 99,28% . . 99,94% . . 100,0%
10+ . . 16,67% . . 62,50% . . 90,28% . . 98,38% . . 99,82% . . 99,99%
11+ . . 08,33% . . 50,00% . . 84,10% . . 96,76% . . 99,55% . . 99,96%
12+ . . 00,00% . . 37,50% . . 76,08% . . 94,12% . . 99,01% . . 99,88%
13+ . . 00,00% . . 25,00% . . 66,44% . . 90,20% . . 98,03% . . 99,72%
14+ . . 00,00% . . 15,74% . . 55,40% . . 84,80% . . 96,41% . . 99,39%
15+ . . 00,00% . . 09,26% . . 44,14% . . 77,80% . . 93,92% . . 98,79%
16+ . . 00,00% . . 05,09% . . 33,56% . . 69,41% . . 90,34% . . 97,79%
17+ . . 00,00% . . 02,78% . . 24,38% . . 60,03% . . 85,52% . . 96,21%
18+ . . 00,00% . . 02,78% . . 17,05% . . 50,26% . . 79,42% . . 93,87%
19+ . . 00,00% . . 02,78% . . 12,27% . . 40,74% . . 72,17% . . 90,61%
20+ . . 00,00% . . 02,78% . . 09,41% . . 32,29% . . 64,06% . . 86,32%

Playing it the safe way seems to be close to the logic I wielded before:
- 1 dice for cast values up to 4.
- 2 dice for cast values up to 7
- 3 for values up to 10.
Or, in short: (cast value) / 3, rounded. It basically doesn't need the extra dice for insurance :)

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"I move unseen. I hide in light and shadow. I move faster than a bird. No plate of armour ever stopped me. I strike recruits and veterans with equal ease. And all shiver at my coldest of whispers."
- The stiff breeze


Wed Feb 06, 2013 3:14 pm
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