Hello Sally, 算盘 suan4pan2 = "Abacus". "Abaci" is the the plural of "Abacus",so it applies also since words don't have plural in Chinese. "Counting frame" is the description of this machine or tablet. So the 3 of them give the meaning, but you are going to use 'abacus' and 'abaci' in singular and plural.

I thought the plural form of Abacus is "Abacuses". I didn't know "Abaci" is also plural form. oh... I see.