ADS8867: LSB, offset error and gain error

Part Number: ADS8867

Tool/software:

The ADS8867 is a 16 bit which has a very low LSB, about 70uV.

This value is very small compared with the offset error and gain error of the chip, even the typical parameter.

Does this mean if I want an accurate ADC output, the calibration should be done firstly during the sampling every time? or just do the calibration after the power on?