Assumming the ADC input is linear

can you not divide the span (1.8V) by the number of steps (25) and then each time the input varies by 0.072 of 1V (1/25 of the span) you update the display so a 3V input would read

3 - 2.72 = 0.28V / 0.072 = 3.889 for the display,

Obviously you would have to scale all of the numbers to some other factor if you wanted to use purely integer math but you get the idea, the only number

Marshall