Rules question - d10 Roll

[rickier65]

Being somewhat slower than most you you folks, I'm slowly getting therough the manual. The manual describes the d10 roll (which is pretty clear), until it starts discussing what happens when you roll a 1 or a 10. OK, I understand checking whether it's under 1 or over 10, but what is the import of "extending the range by -5 to -4? or by +5 to 15?

I understand, roll 1 get another roll and based on that roll maybe subtract 5 to get a die roll of -4, but do any of the probability table go below 1? (or even 0?).

Not sure I uderstand what the -4 means.

I know some of you folks know these rules backwards and forwards so maybe you could explain? (Maybe even with an example?)

Thanks
Rick

[Mobius]

Each number 1 to 10 has a 10% chance of being rolled. And the numbers 2 through 9 are just what they are.  But once you roll a '1' there is another roll of the d10.  The second number rolled is what is we call the 'backed' number.  
Each second roll (backed number) has an equivalent value.  If the backed roll is any of the numbers 6 -10 it is said to be rolling a '1'.  Since this is half of the 10% chance of rolling a '1' on the d10 there is a 10%/2 = 5% chance of rolling a '1'.
What is left are 5 more numbers.  We call these '-4', '-3', '-2', '-1' and '0'.  To get a '-4' you have to roll a backed number of '1' and only '1'.   Thus there is a .1 x .1 =.01 (in percentage terms 1%) chance of rolling a '-4'.

This type of system produces a scale with 10% chance steps in the middle of the probability curve but with ends that taper down to 1% chance steps.

[rickier65]

Mobius,

Thanks, you were actually the one I was hoping would respond, since you seem to know the rules tables really well. I actually understood the math. What I dont understand is what the negative numbers are used for. the to hit numbers I've seen so far all go from 1- 10.

So what difference doees it make if it's a -2 or a -4. (how is it better than a 1). Sorry to be dense.

Thanks,
Rick

[Mobius]

ORIGINAL: Rick
So what difference doees it make if it's a -2 or a -4. (how is it better than a 1). Sorry to be dense.

A '-4' would be a d10 roll where '1' is backed by a '1'. A '-3' would be a '1' backed by a '2'. A '-2' would be a '1' backed by a '3'.
If a success needed a '-2' or less then '-4', '-3', or '-2' would succeed. (total=3%).
If a success needed a '-4' or less then only -4' would succeed. (total=1%).

It's the 'or less' that shows that the chances are to be added. If success meant 1 or less then all the chances to roll 1 or less would be added up and would total 10%.

[Erik Rutins]

ORIGINAL: Rick
What I dont understand is what the negative numbers are used for. the to hit numbers I've seen so far all go from 1- 10.

Well, for example, lets say your unit is a Soviet Rifle Squad engaging a German Rifle Squad 250m away that's in some light woods. Firepower checks require you to roll equal to or under your firepower to do damage, so the higher your firepower the more you are likely to do. At 250m, a Soviet Rifle squad starts at Firepower -2. That means it would need to roll a -4, -3 or -2 to cause casualies. The Light Woods the German unit is in would further change its firepower to a -3, so it would actually need a roll of 1 followed by a roll of 1 or 2 to get the -3 or -4 result.

Regards,

- Erik

[Deride]

As the developer who implemented the very original set of rules into the battle engine, I can tell you that it took me a while to think through all of this myself. So, I can understand some of the basic confusion around this. But, the explaination from Mobius above is a great way to explain and think about it. You are basically creating a nice bell curve like set of probabilities with just two dice rolls.
 
Deride

[rickier65]

Thanks for your patience all. I get it.

Rick