According to the Wiki, a base reluctance - is worth -2 and ++ can indicate a range from 1,5 to 2,4. How much a third + is worth is unknown.
Why can't we have a precise breakdown like in later titles, EU4 and HoI4? It shouldn't be too difficult of a task transplanting this bit of a code into CK2 or changing the existing bit.
This is ultimately a game of numbers, and arbitrarily hiding and obfuscating them is not fun.
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