THAC0 by the numbers: Difference between revisions
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This article attempts to demystify the dreaded '''THAC0''' ((cue ominous music)) and the other various ways to decide TO-HIT rolls. | |||
'''''SPOILER: THERE WILL BE MATH''''' | |||
Alright, lets get to the meat of this thing. Most of you reading this are familiar with the 3rd edition (D20) way of determining TO-HIT successes. This goes something like this: <br> | |||
:Determine AC of opponent | |||
:Roll 1d20 | |||
:Add Base Attack bonus | |||
:Add modifiers (strength, magic weapon, etc) | |||
:compare total to opponent's Armor Class. | |||
::If larger then hit | |||
::Else miss | |||
<Br> | |||
<br> | <br> | ||
'''EXAMPLE:'''<br> | |||
Bob has a BAB of 1 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 12. Bob rolls an 8 on his D20, adds in his BAB and sword bonus. ((8+1+1=10)) well 10<12 so bob misses the little bastard. | |||
<br> | <br> | ||
<br> | <br> | ||
Pretty straight forward right? yeah! absolutely! well lets take a look at THAC0...<br> | |||
Firstly, THAC0 was introduced in later 1st Edition supplements as a way of speeding up the use of To-Hit tables. yeah guys, this all used to be written up in tables....<br> | |||
so, instead of having a hit table written out for all the various Armor class values from -10 to +10 they decided it would be easier to remember the number needed to hit an AC or 0 and calculate from there.<br> | |||
the calculation goes something like this:<br> | |||
:Subtract targed AC from THAC0 | |||
:Roll 1d20 | |||
:Add modifiers (magic weapon, etc) | |||
:compare total to adjusted THAC0. | |||
::if LARGER then hit | |||
::else miss | |||
<br> | |||
<br> | |||
'''EXAMPLE:'''<br>0 | |||
Bob has a THAC0 of 19 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 8. Bob rolls an 8 on his D20, adds sword bonus. 19-8=11 well 9<11 so bob misses the little bastard. | |||
<br><br> | |||
Ultimately while these methods are different in their execution they are equally simple. the most important thing to remember is that AD&D AC-0 == 3rd ed. AC-20. both systems start with AC-10 as their base. | |||
((basically having a THAC0 of 19 == BAB +1)) | |||
<br> | |||
quick equation comparison:<br> | |||
'''''MAY CONFUSE YOU MORE! IGNORE IF YOU DON'T LIKE MATH!''''' | |||
<br> | |||
AD&D: (THAC0-AC)<= (1d20 + modifiers) | |||
3rd ed.: (1d20 + modifiers) >= AC | |||
<br> | |||
if we flip one equation we get the following: | |||
<br> | |||
AD&D: (1d20 + modifiers)>=(THAC0-AC) | |||
3rd ed.: (1d20 + modifiers) >= AC | |||
<br> | |||
we can then convert the AD&D equation into terms more closely aligned to the 3rd ed mind by treating the AC as a modifier to your d20 roll. | |||
<br> | |||
AD&D: (1d20 + modifiers)+AC >= THAC0 | |||
3rd ed.: (1d20 + modifiers) >= AC | |||
<br> | |||
'''EXAMPLE:'''<br> | |||
Bob has a THAC0 of 19 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 8. Bob rolls an 8 on his D20, adds sword bonus. (8+1)+8=17 well 17<19 so bob misses the little bastard. | |||
Latest revision as of 10:38, 21 October 2013
This article attempts to demystify the dreaded THAC0 ((cue ominous music)) and the other various ways to decide TO-HIT rolls.
SPOILER: THERE WILL BE MATH
Alright, lets get to the meat of this thing. Most of you reading this are familiar with the 3rd edition (D20) way of determining TO-HIT successes. This goes something like this:
- Determine AC of opponent
- Roll 1d20
- Add Base Attack bonus
- Add modifiers (strength, magic weapon, etc)
- compare total to opponent's Armor Class.
- If larger then hit
- Else miss
EXAMPLE:
Bob has a BAB of 1 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 12. Bob rolls an 8 on his D20, adds in his BAB and sword bonus. ((8+1+1=10)) well 10<12 so bob misses the little bastard.
Pretty straight forward right? yeah! absolutely! well lets take a look at THAC0...
Firstly, THAC0 was introduced in later 1st Edition supplements as a way of speeding up the use of To-Hit tables. yeah guys, this all used to be written up in tables....
so, instead of having a hit table written out for all the various Armor class values from -10 to +10 they decided it would be easier to remember the number needed to hit an AC or 0 and calculate from there.
the calculation goes something like this:
- Subtract targed AC from THAC0
- Roll 1d20
- Add modifiers (magic weapon, etc)
- compare total to adjusted THAC0.
- if LARGER then hit
- else miss
EXAMPLE:
0
Bob has a THAC0 of 19 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 8. Bob rolls an 8 on his D20, adds sword bonus. 19-8=11 well 9<11 so bob misses the little bastard.
Ultimately while these methods are different in their execution they are equally simple. the most important thing to remember is that AD&D AC-0 == 3rd ed. AC-20. both systems start with AC-10 as their base. ((basically having a THAC0 of 19 == BAB +1))
quick equation comparison:
MAY CONFUSE YOU MORE! IGNORE IF YOU DON'T LIKE MATH!
AD&D: (THAC0-AC)<= (1d20 + modifiers)
3rd ed.: (1d20 + modifiers) >= AC
if we flip one equation we get the following:
AD&D: (1d20 + modifiers)>=(THAC0-AC)
3rd ed.: (1d20 + modifiers) >= AC
we can then convert the AD&D equation into terms more closely aligned to the 3rd ed mind by treating the AC as a modifier to your d20 roll.
AD&D: (1d20 + modifiers)+AC >= THAC0
3rd ed.: (1d20 + modifiers) >= AC
EXAMPLE:
Bob has a THAC0 of 19 and is wielding a +1 sword of doom. he swings at random cowering goblin A who has an AC of 8. Bob rolls an 8 on his D20, adds sword bonus. (8+1)+8=17 well 17<19 so bob misses the little bastard.