By means of this spell, the priest can accurately estimate the chance of
success of one specific action, such as climbing a dangerous cliff, making a trick
bowshot, crossing a burning room unharmed, or even striking an enemy. The action
in question must be one that would normally be resolved by a die roll, but the
priest doesn’t have to be the person who attempts the feat; he can use calculate to estimate the odds for anyone taking an action in his sight. The priest has
a 70% chance, +2% per level, of making an accurate estimate.
If successful, the DM reveals to the player the action’s chance for success or
any modifiers that may be in play. For example, he could reveal a particular
opponent’s Armor Class or THAC0, the saving throw an opponent would require in
order to save against a particular spell cast by the priest or the priest’s
wizard companion, or a character’s chance to open doors, bend bars, or use a thief
ability. The priest could even calculate his odds for actions that might be resolved by a die roll or DM caprice, such
as his chance to avoid detection by hiding behind a rock. This spell takes into
account factors that the priest himself may not be aware of, so from time to
time a character may receive some very confusing results from this spell. For
instance, if the priest doesn’t know that an orc chieftain is actually a
polymorphed tanar’ri masquerading as an orc, he may be astonished to learn that the
“orc” has a THAC0 of 7!
If the priest fails his calculation check with a roll of 99 or 00, his
calculation is wildly skewed in a random fashion. The material component for this
spell is a miniature abacus of ivory worth at least 100 gp. It is not consumed in
the casting of the spell.
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