Another bad tutorial.
You never will get an ACS712 to play nicely with an ESP. An ACS712 has a ratiometric output that needs a ratiometric A/D, which the ESP doesn't have (An Uno R3 does). With an ESP, current and zero point also depend on supply voltage of the ACS. If you want to get it sort-off ok, then you also need to measure ACS supply voltage, and add that variation to the current equation.
Leo..
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