Logic Masters Deutschland e.V.

Rules:
Sudoku: Place the digits 1-9 into each row, column and outlined 3x3 box without repeats.
Loop: Draw a one-cell wide loop into the puzzle. The loop may only move orthogonally from cell to cell, does not branch or cross itself, and does not touch itself orthogonally or diagonally. Within each box, adjacent digits on the loop must differ by exactly N, where the value of N is different in each box visited by the loop. No restriction applies when the loop crosses box borders. If the loop enters a box it must take at least two cells there, so that a valid difference of N can be built.
Diamonds: A diamond in a box indicates that the box with the diamond is visited by the loop. The value in the diamond cell shows the difference value N of that box's loop segment. Diamonds may or may not be visited by the loop.
Difference: Cells separated by a white dot are consecutive. Not all white dots are necessarily given.

Links: You can solve the puzzle in the CTC Software.