Puzzle: Place seven discs so they are inequidistant

The task is to place seven discs onto this matrix, one disc per cell, in such a way that each disc is separated from all the others by a different distance measured vertically, horizontally, diagonally or obliquely in any direction.

Since the probelm is a difficult one (there are 21 disc pairings altogether), three discs have already been placed.

Theory has it that such a unique all-different layout can be achieved only where the number of discs involved is the same as the order of the grid.

See the answer to place seven discs so they are inequidistant.