ESP8266 AnalogRead value mismatch

Hi friends i try to measure Battery voltage in ESP8266 ADC pin but analogRead(A0) function not measure accurate Input value.



A0 input voltage is 0.903v but analogRead(A0) function print 984 it's 80 mismatch.

how can i get accurate value input value to Serial.print....???

the voltage sensed by the pin is 984/1024. but that is still not 0,90

This is i get actual reading

Multimeter(volt) ADC (count) ADC (volt)
0.939 986 0.963
0.856 921 0.899
0.769 836 0.816

how to get ADC volt as like as multimeter exact volt ...???