have you not a manual? hehe anyway first and foremost the definition.
ToHitArmorClass 0. this is the basis on when you are to hit an opponent. you add/subtract(i forgot)your Thac0 to the Ac of you opponent for example your Thac0 is 2. the opponents AC is -4. add and you get -2. so that means you only need a -1 and above to hit. meaning it hiys all the time except when its critical miss...
better read the manual.
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We have merged... and now we are called Chiharumut..wehehehe