From THAC0 to HERO

[ronpyatt]

My group recently starting playing with the HERO system (6E), and I've been teaching them how to play. One of my players recognized the attack roll pattern as too similar to the dreaded THAC0. When I broke out a chart, eyes rolled.

 

I know there are several methods to presenting the formula, but I'm looking for an easy way to present the values by simplifying the process and removing some element of the formula without relying on a chart.

 

The number 11 is the only universal constant in this formula. Since I have a lot of players with D&D background, I thought I'd use the 11 to create a pre-calculated Combat Defense number (similar to Pathfinder's CMD or AC), which would be 11-DCV = CD, and making that CD a regular part character sheet. Since the target number would be CD or less, the attacker's to hit would be simply 3d6 - OCV.

 

Positive modifiers increase the CD, and negative modifiers decrease the CD.

 

Am I calculating this correctly?

[ghost-angel]

Re: From THAC0 to HERO

 

Just use this: 11 + OCV - 3D6 = DCV Hit.

 

You can even write it thusly; assume OCV of 6

Combat Skill = 11 + 6 = 17-

So you have a Combat Skill of 17-.

 

If you roll a 10 on 3D6:

17 - 10 = Hit DCV 7 or less.

 

You can apply modifiers directly to that number after rolling as well. If you have a Range Modifier of -2, and +3 Combat Skill Levels:

7 - 2 + 3 = Hit DCV 8 or less.

[prestidigitator]

Re: From THAC0 to HERO

 

Flipped Die Rolls

 

I've modified this method even further lately. What I do now for Skills is: Familiarity buys you a flat -1 modifier on your roll; purchasing the full Skill buys you a +0, and you increase it from there; when you have the full Skill and you roll it you always combine it with either a Characteristic modifier, or +2 if no Characteristic is appropriate for the task at hand (Familiarity doesn't grant you either the Characteristic modifier or the +2). For example, if you're trying to quickly haul yourself up the side of a cliff with a rope, you might roll 3d6+Climbing+Str to see how quickly you do it. If you're trying to climb the cliff without a rope in slippery conditions, you might roll 3d6+Climbing+Dex to see if you make it at all. If you only have a Familiarity with climbing, you'd roll 3d6-1 either way.

[ronpyatt]

Re: From THAC0 to HERO

 

Just use this: 11 + OCV - 3D6 = DCV Hit.

 

You can even write it thusly; assume OCV of 6

Combat Skill = 11 + 6 = 17-

So you have a Combat Skill of 17-.

Yeah, taking out the 11 from the calculation every time is exactly what I'm looking for. Combat Skill (which I will call Base Attack) of (11+OCV)- would work great. It's the opposite of what my players are used to seeing with the defensive value calculated like Armor Class, which was where I was going with Combat Defense, but your suggestion has the advantage of avoiding a negative defense value.

 

I'll try using this Base Attack value. It still feels a bit clunky, but if I can just get them around that we should be fine.

[ronpyatt]

Re: From THAC0 to HERO

 

Flipped Die Rolls

 

I really like the flipped die rolls method. It's intuitive and familiar, but I want to stick with the HERO convention. Once the players get used to the roll low they'll be in line with the rest of the HERO community. That way, if they go to another HERO game they won't get laughed at.

[Killer Shrike]

Re: From THAC0 to HERO

 

It's not really like THAC0, it's an expression oriented around the bell curve and is entirely about actually hitting. THAC0 on the other hand was a hack to get around a flawed inverted "AC" model that measured amount of mitigation as a chance to effectively convert a hit into a miss.

 

In the HERO System, all things being equal you hit on an 11- which is 62.5% of the time.

 

attackers OCV- defenders DCV = modifier to 11-

 

Its as simple as that.

 

Personally, I go with the (11+ OCV) - 3d6 = DCV hit formula myself.

[ghost-angel]

Re: From THAC0 to HERO

 

Yeah, taking out the 11 from the calculation every time is exactly what I'm looking for. Combat Skill (which I will call Base Attack) of (11+OCV)- would work great. It's the opposite of what my players are used to seeing with the defensive value calculated like Armor Class, which was where I was going with Combat Defense, but your suggestion has the advantage of avoiding a negative defense value.

 

I'll try using this Base Attack value. It still feels a bit clunky, but if I can just get them around that we should be fine.

 

The advantage to calculating the value beforehand and adding Skill Levels (and other modifiers) to the result is that it looks exactly like the Hero System Skills in convention (if not specific formula).

 

Attacking and Skill Rolls really are the same mechanic: trying to get as high a success as possible by rolling as far under a number as possible.

[ronpyatt]

Re: From THAC0 to HERO

 

It's not really like THAC0.

 

Personally, I go with the (11+ OCV) - 3d6 = DCV hit formula myself.

 

Exactly.

 

I mentioned THAC0 because it represents the terror old D&D players feel when they encounter the HERO System's to-hit formula. I've witnessed it too many times to deny it.

 

And, yes, I'll be trying the Base Attack - 3d6 = DCV or less method.

[ronpyatt]

Re: From THAC0 to HERO

 

That 11+OCV really kills it for a lot of players. I've see the same thing happen in D&D when calculating the DC for resisting a spell, where players are constantly repeating, "how do you calculate the DC?" It's better to include the constants like we do with Skill Rolls, because constants are not going to change. No need to keep adding 11 when it's already added into the value.

[torchwolf]

Re: From THAC0 to HERO

 

That 11+OCV really kills it for a lot of players. I've see the same thing happen in D&D when calculating the DC for resisting a spell' date=' where players are constantly repeating, "how do you calculate the DC?" It's better to include the constants like we do with Skill Rolls, because constants are not going to change. No need to keep adding 11 when it's already added into the value.[/quote']

While it's true that OCV is a constant value, there are modifiers in the combat system that will occasionally halve the OCV or the DCV. While this will not be a problem with the DCV, you will need to address the OCV halving.

Option 1) Just list the value for half OCV separately, as the modifier to be subtracted from the [11+OCV] value whenever this occurs. You might want to adjust this number, as the Rules As Written apply halving of the OCV or DCV after all other modifiers have been applied.

Option 2) Figure out the average OCV in the campaign and use half of that as the flat negative modifier to [11+OCV]. In this case, you might want to do the same with DCV halving. Again, you might want to adjust this number because of the reasons given under Option 1.

Option 3) To simplify, disregard all of the above, and just halve the total of [11+OCV] including all modifiers (i.e., if [11+OCV] is 17, applying other positive and negative modifiers totaling (for example) +2, resulting in a value of 19, halving this and rounding up results in a halved modified total of 10, from which the DCV of the target is then subtracted). While this does not exactly produce the same probabilities as the Rules As Written, it is consistent.

Option 4) If OCV is halved by circumstances or Maneuvers, subtract 11 from the [11+OCV] and halve the remainder. This option most closely approximates the Rules As Written and will probably maintain game balance best.

 

There have been some discussion on applying flat modifiers instead of halving, both concerning OCV and DCV. A forum search should turn these threads up. I believe some of those responding to this thread have participated in those discussions as well, so do listen to their suggestions, especially considering probability concerns.

 

Wish you luck with this, and the Hero System!

[gojira]

Re: From THAC0 to HERO

 

Positive modifiers increase the CD, and negative modifiers decrease the CD.

 

Am I calculating this correctly?

 

 

I think it should be the other way around, positive modifiers should decrease CD. You are basically re-inventing the original Armor Class system, where better defense is represented by a lower number.

 

For example:

 

DCV 5 vs DCV 10.

 

11 - 5 = 6

 

11 - 10 = 1

 

Which is the better number? 1 is, because it represents the higher DCV. There's more than one way to skin this cat, but generally folks use systems like Ghost Angel's: Precalcualate the To-HIt roll (11+OCV) then use that to modify the players roll vs a random DCV.

 

If this doesn't work for you however, please come back and tell us, there's at least a couple more major ways to finesse the system, with out actually changing the rules.

[ronpyatt]

Re: From THAC0 to HERO

 

Very good stuff. Thanks for all the feedback.

 

I'm not looking to change the system's math or types of rolls. I'm looking for ease of use. With the 11+OCV being constant per character, the other constants such as Half OCV or 0 OCV, should also be pre-calculated with the +11 and sitting on the sheet ready for use. If those pre-calculations have a proper name then all the better. If there are any modifiers that are not constants they can be added on the fly to the Base Attack, which makes it easier as those variables are outside the player's sense of character-self.

 

I'm looking to introduce the system to new players, and the moment I throw out the To-Hit, I want lights to go off with one of those "AH-HA!" moments and not groans to fill the room.

 

Something like these Virtual Stats:

Base Attack = 11 + OCV

Half Base = 11 + Half OCV

Un-Prepped = 11 + 0 OCV

 

With the caveat: Virtual Stats cannot be directly affected by powers.

 

This is at least until I can get them to know the system enough to find out how it all works... if they want.

[Hugh Neilson]

Re: From THAC0 to HERO

 

Something like these Virtual Stats:

Base Attack = 11 + OCV

Half Base = 11 + Half OCV

Un-Prepped = 11 + 0 OCV

 

With the caveat: Virtual Stats cannot be directly affected by powers.

 

You might want to customize character sheets to include these in a combat block. They're easy enough to derive from OCV. The Virtual Stats would not be directly affected by powers, but would move with OCV modifiers. OCV can be affected by powers, but more comonly by situational bonuses or penalties (eg. Range, Surprise, Growth), bonuses or penalties for specific combat maneuvers and combat skill levels.

[Sean Waters]

Re: From THAC0 to HERO

 

If you want THACO (I'm sorry, what edition are you using?) for 3rd or 3.5 ed DnD, in Hero, do this:

 

DCV (or armour class) +10 = Target number for 3d6+OCV (or plus to hit)

 

The maths is identical to low roll: you still hit 62.5% of the time all other things being equal.

 

Although it is mathematically identical, some people just 'get' it more intuitively that way around, possibly just to upset long term Hero players. I'd go with whatever is easiest, which, for most people, is 'big number good, small number bad'.

[Susano]

Re: From THAC0 to HERO

 

Personally, I go with the (11+ OCV) - 3d6 = DCV hit formula myself.

 

I use this formula. The advantage is, the GM never needs to tell the players the DCV of anything. The players can tell him what they hit all on their own.

 

I've also boiled this formula down to 11 = my OCV, each +1 or -1 moves the value up and down by one. So If I have an OCV of 10 and roll and 1, I hit a DCV of 10. If I roll a 12, I hit a DCV of 9, if I roll a 10, I hit a DCV of 11 (and so on.)

[Alcamtar]

Re: From THAC0 to HERO

 

I use 3d6 + OCV - 10 >= DCV

Mathematically equivalent and dead simple.

 

Note that in formulas based on 10 instead of 11, you want to roll high not low.

 

Really it's identical to how d20 works:

• dice = 3d6 instead of d20
  
• BAB = OCV
  
• AC = 10 + DCV
  
• roll high to succeed
  

[Hierax]

Re: From THAC0 to HERO

 

Yeah,

 

DCV+10=AC (Avoidance Class)

 

3d6 + OCV = AC Hit (Hero)

 

d20 + to Hit Bonus = AC Hit (d20/3.x D&D)

[Hierax]

Re: From THAC0 to HERO

 

Also, if you want to vary it a bit you can do an opposed roll:

 

3d6 + OCV vs. 3d6 + DCV

 

Basically you reverse the "Take 10" process from d20 to get a d20 for a 10 roll, it's like Hero's Standard Effect-ish (yes I know it's not totally equal).

[Zane_Marlowe]

Re: From THAC0 to HERO

 

When I came to Hero System, I'd been playing Warhammer 40k most recently, and the to hit numbers were very intuitive in that light. Here's a simple rule you can teach new players if you're not obsessed with keeping DCV values secret.

 

If OCV and DCV are equal, then the to hit number on 3d6 is 11. If they differ, adjust the target number in favor of the person who has the higher value by the amount of the difference. Bob has OCV 5 and Alice has DCV 5, so target is 11. If Alice dodges, increasing her DCV by 3, then Bob's target number is 8 instead.

 

Super simple.

[redwulfe]

Re: From THAC0 to HERO

 

The way I always tell people is to roll a check at 11- the amount you make the roll by or miss it adjusts your OCV to the DCV hit. So if I have a OCV of 4 and I roll a 9 then I hit DCV 6 (9-11= 2, 2+ OCV of 4 = 6). this is the same thing they do when they do a skill or perception check. They tell me the margin of error or success. So it becomes very similar to other rolls and this makes it start to become second nature after a while. Even if they go to another GM they can still tell him what DCV they hit and continue to play the game without problems.

 

Red

[Rapier]

Re: From THAC0 to HERO

 

My preferred method is Proportional Adjustment.

 

DCV Hit = OCV + (11 - Roll)

 

or (and Chad always had to do it this way. He was a math/mechanical engineering major so he was always a little off)

 

DCV Hit = OCV - (Roll - 11)

 

Basically, you compare your roll to 11. If you rolled a 9 (2 under 11) you add 2 to your OCV.

 

That has always seemed the simplest to me, but everyone is different. Some people can't count very well in their heads and prefer the chart. Some people have to keep an (OCV + 11) written down somewhere and do the (OCV + 11) - ROLL.

 

There is no all great, perfect method. Everyone is different. And in case they are rolling their eyes, give them a smack. ALL systems use some kind of math to determine if an attack hits. Nut up and get over it.

[Hierax]

Re: From THAC0 to HERO

 

Also using the DCV+10=AC (Avoidance Class) as a contest of OCV vs. DCV (3d6 + OCV vs. 3d6 + DCV) method you can easily reverse things to let the players roll all the dice including the to hits against their own characters:

 

• 3d6 + OCV vs. DCV + 10
  

 

• = 3d6 + OCV vs. DCV + 3d6
  

 

• = 10 + OCV vs. DCV + 3d6
  

i.e.,

 

Attack Roll for Player:

when the PC attacks an NPC he rolls his 3d6 + OCV vs. DCV + 10 (AC) of the NPC;

 

Defence Roll for Player:

when the PC is attacked by an NPC he rolls his 3d6 + DCV vs. the OCV +10 of the NPC.

 

This is a great way to speed up the game and save the GM some dice rolling and get the players more involved in determining their own character's fate.

[AmadanNaBriona]

Re: From THAC0 to HERO

 

 

There is no all great, perfect method. Everyone is different. And in case they are rolling their eyes, give them a smack. ALL systems use some kind of math to determine if an attack hits. Nut up and get over it.

 

Seriously, yeah.

Well said.

I started gaming in the 70's, mostly with wargames, and people complain that HERO math is hard? Most of the functional math that's stuck in my brain was learned trying to understand how some of them were played.

 

You may be a geek when you're caught pondering ballistics equations in the aisle of the grocery store at lunch by your less pre-occupied peers (I was working on the Great Weapons Lists for our pre-Star Hero space opera campaign and had a breakthrough). I'd been playing a lot of Morrow Project & Fringeworthy before that so had all those wacky formulas just oozing around in my brain.