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About this drill
Once both complement families are automatic, the limiting factor is not knowledge — it is stamina. A ten-row column contains roughly twenty bead decisions, and a single lapse anywhere in the sequence destroys the answer with no warning and no way to spot it afterwards. This is the level where children learn that abacus accuracy is a property of attention, not of arithmetic.
Practise these at a steady rhythm rather than as fast as possible. Speed on long columns comes from never stopping, not from moving quickly — a learner who works at a metronome pace and never re-reads a row will beat a faster one who hesitates twice.
How to practise it
1Set a steady beat — one row per beat, out loud or with a metronome.
2Never re-read a row you have already added.
3If you lose the total, stop and restart the column; do not guess.
4Check the answer once at the end, not partway through.
It is the standard column length in abacus examinations and competitions, long enough to test concentration and short enough that a mistake does not cost several minutes.
Should the running total be checked partway?
No. Checking mid-column trains the habit of doubting, which costs more accuracy over time than the occasional lost problem.
Is this still done on beads or in the head?
On beads at this level. Mental visualization starts properly at the next stage, once ten-row accuracy on the physical abacus is reliable.
How many columns per session?
Eight to ten is plenty. Long-column work is tiring in a way single-digit drills are not, and accuracy collapses well before boredom does.