When I saw the title of this thread, I though it would be about using a Soroban, not how they are made. I have one (along with some elderly slide rules) and sorta "got into it" many years back. For simple calculations they can be faster than a calculator. It's basically muscle memory, like playing a musical instrument. After enough practice it's quicker to flick the beads than to press the keys on a hand held calculator - which explains the fact that they are still in wide use and being produced in the quantities shown in the video. (But today I do mostly just use a calculator!)