Four Four by Four: Four Sudoku Puzzles Again!

Today's Puzzle:

Four quick puzzles for a Friday to keep us all on our toes. Different logic for each one ☝️

Puzzle 1:

Tiny Regionometer by Michael Lefkowitz https://tinyurl.com/SudokuSleuthRegionometer

Rules 1:

Normal 4x4 Sudoku rules apply.

REGIONOMETER - The box borders divide the grey line into segments, whose sums must increase in one direction along the line.

Puzzle 2:

Perfect Squares by Michael Lefkowitz https://tinyurl.com/SudokuSleuthPerfectSquare

Rules 2:

Normal 4x4 Sudoku rules apply.

Every cage sums to a perfect square.

Puzzle 3:

Do Not Go Gentle by Michael Lefkowitz https://tinyurl.com/SudokuSleuthDoNotGoGentle

Rules 3:

Normal 4x4 Sudoku rules apply.

KROPKI - Digits separated by a white dot have adjacent values. Digits separated by a black dot are in a 2:1 ratio.

KNIGHTS - Odd digits never see another of the same digit a knight's move away. Even digits always see at least one of the same digit a knight's move away.

Puzzle 4:

Why Sum? by Michael Lefkowitz https://tinyurl.com/SudokuSleuthYSum

Rules 4:

Normal 4x4 Sudoku rules apply.

Y SUMS - Numbers outside the grid are the sum of the first Y digits along the row or column, where Y is Yth digit in the row or column starting from the clue. A question mark stands for some number. Not all possible Y-sum clues are necessarily given.