Calculation With Abacus
A pearl calculation is calculations you do with pearls. If you think about using pearls to calculate something, it's going to look a lot like using an abacus. That's why this calculation is calculation with abacus.
しゅざん
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own. Watch out for the rendaku.
今日は珠算を勉強するって気分じゃないんだよね。
I don’t feel like studying calculations on an abacus today.