The double consonant rule applies when you add

The double consonant rule applies when you add a suffix beginning with a vowel to a base word ending with consonant + vowel + consonant. Examples include adding -ed, -ing, -er, and -est to words. Words like bigger or biggest fit here.

i suggest it is anadiplosis

a constant variable, normally called a controlled variable, is the term for a variable that remains constant throughout an experiment, though other variables may change. an example is the water pressure for a faucet when measuring the amount of water released when the faucet is opened to various increments.