fluffy,
there can be a lot of differences, depending on your scale and level of incubation.
To keep it simple, you can use multi-stage parameters as this would be easier for you.
Use 99.5 for the first 25 days with a humidity of about 50-55%. for the last 3 days, drop to 98.5 F and increase your humidity to about 60-65%.
Depending on the duck eggs of course, most duck breeds will take about 28 days. Muscovies, about 35 and mulards, 32. I find that the spread of the hatch is a bit longer with ducks than chickens.
use those parameters and you'll be fine. if you have a high level incubator then and can accurately control humidity and carbon dioxide, i can give you a better parameter scheme that i found to increase my hatch rate by about 11%.
hope this helps.