Surface Pair

Extreme Used by Smart Hint

Two overlapping groups of runs differ by two cells — subtracting their clue totals fixes those cells' sum (or difference), ruling out any digit with no possible partner.

Cells that establish the pattern
Where the conclusion lands
Digit ruled out

How it works

Same subtraction as Surface Sum: the down clues total 16 + 11 = 27 over the tinted block, the across clues total 13 + 24 = 37 over that block plus the row's last two cells.
So those two cells add to 37 − 27 = 10 — even though neither is pinned down yet.
The right-hand one sits in a 4-in-two down run, so it's a 1 or a 3. Its partner must therefore be 9 or 7.
Strike 3 and 5 from the left one. A pair sum is weaker than a placement, but it prices two cells against each other from clues alone.