A thermometer marked in one-degree increments has a mark for every temperature: 1°F, 2°F, 3°F, 4°F, 5°F, etc. A thermometer marked in two-degree increments has marks that skip every other temperature: 2°F, 4°F, 6°F, 8°F, 10°F, etc. Both of those styles are acceptable. However, a thermometer marked at three or more increments (3°F, 6°F, 9°F,12°F,15°F, etc.) is NOT acceptable because its NOT close enough to the exact temperature.