First introduced in Pokémon Diamond and Pokémon Pearl. Characteristics is the one stated under the Pokémon's level when it was first met. It is very helpful in knowing your Pokémon's highest IV. But it can be complicated when 2 or all of your Pokémon's IVs are equal since each characteristics corresponds only to one stat and only one characteristic is shown on your Pokémon's details. So it is still best to consult an IV Calculator, but it maybe helpful sometimes. Below is the link of characteristics and the value of IVs they correspond.
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