The resolution of an ADC determines how many steps it takes between the minimum and the maximum input value. This is specified by number of bits resolution, such as 8bits or 12bits. An 8bit converter takes 256 steps from minimum to maximum
2^{8} = 256
If you wish to measure a 010V signal and you require an accuracy of 0.25%, we will initially consider an 8bit analog to digital converter
010V divide by 256 = 0.03906V steps
Accuracy required 0.25% = 0.025V. Therefore we can see that the size of steps is larger that the accuracy required so it is not possible ensure the accuracy with 8bits resolution
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A 12bit ADC may enable the desired accuracy to be met. 2^{12} = 4096 steps.
When we divide 10V by 4096, it equals 0.0024V, which is 10 times smaller that the required accuracy.
A 16bit ADC will provide 2^{16} steps = 65,536, so on a 10V signal we can see steps of 0.153mV.
Please note  these calculations only look at resolution of analog to digital conversion, and do not include errors caused by component tolerance, temperature drift and other adjustment errors that make up measurement accuracy. 