Slice oranges 1/8-1/4 inch thick. Discard (compost) the end slices that are all peel.
Remove any seeds.
To oven dry, place slices into a 200 F oven on a baking sheet topped with an oven safe metal rack or parchment. Flip slices over every hour until dry. Time will vary based on thickness, tightness of the oven seal, and will be less if you have a rack (since they can dry from both sides at the same time). Mine took 4-6 hours on parchment. On a rack, it should be about half that.
To dry using a dehydrator, set the temperature to 135F. Set the slices on a mesh drying sheet. If you are worried about dripping, pat them dry first or set up an additional, unused tray with a solid drying sheet below. Start the dehydrator and flip the slices every hour or so. Mine have taken from 6-9 hours on a mesh tray but double the one time I used a solid tray.
I am not a health professional and nutrition data is calculated programatically. Accuracy may vary with product selection, calculator accuracy, etc. Consult a professional for the best information.