ADC errors

[Nasib]

hi i am using this to capture the adc value 

data_ADC=adc_buffer[1]*(1024+gain_error) / 1024 + offset_error - 0.5;

data_ADC_double=data_ADC*3.6/1024;


MULTIMETER MEASUREMENT: 1.72V

ADC RESULT: 1.65V 

Could anyone help me please?