Preparation
Print out, preferably on to card, and cut at horizontal line to remove heading. Cut in from top and right to remove area shown as white space on image. The L-piece is ready.

How to use
The bottom markings are spaced to align with the same digit in arrays along a row, and the side markings in arrays down a column. When an array is promoted, the L-piece can be used to locate the particular digit for elimination from other arrays. The shaded section helps with cells.

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