The abacus has an advantage of not requiring a writing implement and paper (needed for algorism) or an electric power source.
ðɪ ˈæbækəs hɐz ɐn ɐdvˈæntɪdʒ ʌv nˌɑːt ɹᵻkwˈaɪɚɹɪŋ ɐ ɹˈaɪɾɪŋ ˈɪmplɪmənt ænd pˈeɪpɚ nˈiːdᵻd fɔːɹ ˈælɡɚɹˌɪzəm ɔːɹ ɐn ᵻlˈɛktɹɪk pˈaʊɚ sˈoːɹs.