i think the tutorial explain it all. this action
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Multiboard - Set the width for (Last created multiboard) item in column 1, row 2 to 10.00% of the total screen width
just like ruleronfiron mentioned, when you set the width for column 0, it will affect all columns (column 1, column 2, column 3, ...., column n) and when you set the width for row 0, it will affect all rows (row 1, row 2, row 3,...., row n),