Mathhammer: Scatter dice Probability II

I've been asked since writing my previous article on scatter dice probability how to calculate the probability of a certain distance of scatter, not just a direct hit. This is actually pretty easy to calculate using the same forumla.

How do you calculate the prob of scattering 1 inch or less for a BS of 4?
- Use the same formula I showed you before, but use a BS of 5 instead of 4
- For 2 inches or less use a BS of 6 instead of a 4

That gives me the probability of 1 inch or less, how do I get the probability of just scattering 1 inch?
- Calculate the probability of scattering 1 inch or less, then subtract the probability of not scattering at all, to get the probability of just scattering 1 inch.

Lets go over some examples

To calculate the probability of a blast template scattering 2 inches or less with a BS of 4
- there are 15 ways to roll a 6 (BS of 4+2) or less on 2D6
P = ( 1/3 ) + ( ( 15 / 36 ) * 2/3 ) = .611 = 61% chance of scattering 2 inches or less with a BS of 4

To calculate the probability of a blast template scattering just 2 inches
- Subtract the probability of a blast template scattering 1 inch or less from the probability of scattering 2 inches or less
- P = 61% - 52% = 9%

You can check your results against these

BS of 2
scatter of 0 = 35%
scatter of 1 = 4%
scatter of 2 = 5%

BS of 3
scatter of 0 = 39%
scatter of 1 = 5%
scatter of 2 = 8%

BS of 4
scatter of 0 = 44%
scatter of 1 = 8%
scatter of 2 = 9%

- Hope this helps!

Mathhammer: Scatter dice probability

“Our bombs are smarter than the average high school student. At least they can find Kuwait.” - A. Whitney Brown

A few days ago I started to think of an easy formula people could use for figuring out the probability that a blast weapon would scatter within a certain distance. Here is what I came up with.

How the scatter dice work
- You roll 1D6 in which two sides have a [hit] marker and four sides have an [arrow] for the direction the blast template scatters.
- You roll 2D6 and add the numbers together to see how far the blast template scatters if an [arrow] is rolled.
- Sometimes you can subtract the BS of the shooter from the 2D6 roll.

Here is what we know
- 1 out of 3 times the template doesn't scatter at all due to the [hit] marker.
- 2 out of 3 times the template doesn't scatter if the 2D6 roll is less than or equal to your BS.

So far the formula looks like this
- P=Probability that blast templates won't scatter
- P = ( 1/3 ) + ( chance that 2D6 - BS = 0 )
- the ( 1 / 3 ) is because one out of three times we roll a [hit] on the scatter dice

How do you figure out the odds of a 2D6 roll?
- There are 36 (6*6) different possibilities when rolling 2D6
- Here is a chart that shows how many possibilities there are for each result on a 2D6 Roll

2D6 ROLL --- # Possibilities
2 --- 1
3 --- 2
4 --- 3
5 --- 4
6 --- 5
7 --- 6
8 --- 5
9 --- 4
10 --- 3
11 --- 2
12 --- 1


Now what does the formula look like?
- P=Probability that blast templates won't scatter
- POSS=Number of possibilities 2D6 will be equal to or less than your BS
- P = ( 1/3 ) + ( ( POSS / 36 ) * 2/3 )

Let's go through some examples

What is the probability that a blast template won't scatter, with a BS 4 shooter?
- There are 6 ways to roll a 4 or less on 2D6, 1 way to roll 2, 2 ways to roll 3, and 3 ways to roll 4.
- So plug in the values and you get
P = ( 1/3 ) + ( ( 6/36 ) * 2/3 ) = 0.44 = 44% chance the template won't scatter

What is the probability that a blast template will scatter 2 inches or less with a BS 3 shooter?
- A BS 3 shooter needs to roll a 5 or less on 2D6 to scatter 2 inches or less.
- Thee are 10 ways to roll 5 or less on 2D6, 1 way to roll 2, 2 ways to roll 3, 3 ways to roll 4, and 4 ways to roll 5.
- So plug in the values and you get
P = ( 1/3 ) + ( (10/36) * 2/3 ) = 0.518 = 52% chance the template won't scatter more than 2 inches

What is the probability that my deep striking Necron lord will scatter 8 inches or less?
- You need to roll 8 or less on 2D6 to scatter 8 inches or less.
- There are 26 ways to roll 8 or less on 2D6.
- So plug in the values and you get
P = ( 1/3 ) + ( (26/36) * 2/3 ) = 0.814 = 81% chance of not deep striking more than 8 inches

- I hope this helps everyone, and of course probability for blast template scatter will be in FarseerMobile and FarseerOnline when they are released. Let me know what you think!

FarseerMobile (Mathhammer Calculator) for Blackberry First Beta Complete

The first beta of FarseerMobile for Blackberry is complete and was sent out to the beta testers tonight. What makes the Blackberry version so useful is you can actually use it during a game as getting the results is super fast, all you have to do is plug in three to four numbers and there you have it. I used it while putting together a Necron army list to play against my brothers IG army, and I was very surprised especially by the results of comparing destroyers with heavy destroyers by their expected damage results against vehicles. I ended up taking two units of regular destroyers instead of the heavy destroyers.



I especially like the feature of being able to select each result on the damage chart you want combined into a single probability. The math for combining these is a lot more complicated than just adding the probability of each damage result, as it's a binomial probabilty, so it's really nice to get that number by just checking a few boxes.

I'm working on a screen for blast scatter, and leadership probability, should be done in a week or so. I could still use a few more beta testers, so again if you are interested, just email me and I'll get you setup.

- As soon as the Blackberry release version is complete I'll be starting on a web based version, which shouldn't be too hard as most of the code from the BB version will be reused.

WANTED: FarseerMobile beta testers

Do you play Warhammer 40K? Do you own a Blackberry? If so you might be interested in beta testing FarseerMobile, a new free Blackberry application I've developed for making quick mathhammer calculations. It's simple to use, very fast, and you don't even need to have any mathhammer skills to use it. I plan on having calculations for shooting at infantry, shooting at vehicles, rolled distance moves such as moving through cover etc, and passing or failing moral checks.

So far the beta only includes calculations for shooting at infantry, here is how it works.

Here is what you input,

- Number of shots

- Dice roll needed to hit

- Dice roll needed to wound

- Dice roll needed for target to make an armor / cover / inv save

- Optional dice roll needed for a second save such as FNP or WBB

Here is what it calculates,

- Expected number of unsaved wounds for a single shot

- Expected number of unsaved wounds totaled for all shots

- Probability of the shooting resulting in 0 unsaved wounds

- Probability of the shooting resulting in 1+ unsaved wounds

- Probability of the shooting resulting in 2+ unsaved wounds etc.....

If you are interested in becoming a beta tester just send me an email to benjamin.cauldwell ( at ) gmail.com with the following information,

- Your name

- How long you have been playing 40K and which army do you play the most

- Which model of Blackberry you have

I plan on having a web based version in the future, but I want to focus on the Blackberry version for now since I have one, and it's so portable.

Hope to hear from some eager beta tester soon!