The spelling of the word "set tos" can be explained through the use of IPA phonetic transcription. The first syllable, "set", is pronounced with the vowel sound of "e" as in "bet", followed by the consonant sound "t". The second syllable, "tos", has the same vowel sound as the first syllable, and is followed by the consonant sound "s". Therefore, the correct spelling of the word follows the phonetic sounds of "set-tos".