how can we do calculations mentaly(without kit)?is it that practising on kit will lead to improve visualization(like multiply 4digit X 4digit) or do we need to practise such big numbers mentally to improve visualization (because it seems impossible to do reach such stage of doing complex calculations mentally)?
Please don't double post.
Practicing with a real soroban helps you to improve without the burden to visualize and remember the beads positions.
It's like blindfold chess. You don't try to play chess blindfold, without knowing to play chess, at a good level. Because if you have to think at your next move while keeping track of every pieces, that quite of lot of things to think at once.
Doing anzan with bigger number needs you to memorize the position of more beads. So a good memory will help. If you don't have one, muscle it up.
Being goood at the soroban (the real one), let you know very well the mechanics of beads moving, and that really helps when doing anzan.
I can't give much more advice here, because I do only one digit addition on anzan. Don't even talk me about multiplication there.