Some people use an abacus to do accounting 有些人使用算盘算帐。
using an abacus to do division is a lot more difficult than to do multiplication, at least according to my own experience, particularly when one number is not divisible by the other 以我的经验来说,用算盘计算除数比起计算乘数难得多,尤其当其中涉及不能整除的数字。
It is not difficult to see that this would make calculating interest more convenient if one was using an abacus instead of a calculator or computer . perhaps this is why the tradition was established 试想像用算盘而不是计数机或电脑的话,可以被9整除的利率会使计算利息更方便,说不定这就是被9整除这个习惯逐渐形成的原因。