Everyone's input on this has been very helpful. I think fixed point will work just fine for me. I'm only dealing with daily temperature, so no big dynamic range requirements. I want to display the temperature on an LCD. I'm using a LM34CZ. It outputs 10mv per degree F. On the LCD, I only expect one place after the decimal. (I am probably lucky if I get accuracy to the nearest degree, but it's still nice to have that decimal place to see which way the temperature is trending.) To make it simple for now, I decide to place limits of 0-100 degrees F. Will this design work?: Vcc is 5v. The PIC ADC is configured to use Vcc as the upper ref voltage. Take the 10bit ADC value, multiply it by .00488 (5/1024). That will result in the actual voltage. Multiply that value by 100 to get degrees. (or instead of of using .00488 in the previous step, just use .488) How do I determine what fixed point format will work? The ADC result is 10 bits so I will need at least two bytes. How do you determine how many bits are required for the fractional part after the decimal? On figuring out how many bits I need before the decimal point: Assuming a max temperature of 100 deg F, that results in 1V into the ADC (100 x 10mv). 1V in the ADC would correspond to 204 ( 1/.00488). That 204, I believe will be the largest number, so 8 bits should work. Is this correct logic? Since I need to represent .488, I will need enough bits to hold 488. That ends up requiring 9 bits (2^9=512). Is this the correct way to tell how many bits you need for the fractional part? Maybe for simplicity I should use the 16x16 fixed point format? Or maybe it can be determined that .49 will be accurate enough? Although I don't know how to calculate how accurate that will be. .488 itself is a rounded result of 5/1024*100. Maybe .5 would be accurate enough? On a slightly different topic, since I'm going to hard code the voltage per bit of the ADC, I need a stable and accurate voltage reference. For simplicity's sake, I was going to use Vcc which is 5v. What are some strategies to help guarantee a stable and accurate reference voltage for an ADC? Thanks for all of your input. - Mark Bellamy -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist