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.

Example:

Serial.println(analogRead(A0));

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 ...???

https://www.esp8266.com/viewtopic.php?f=13&t=1324