I have tried a very hard puzzle, got stuck, so went to various Sudoku solver sites which either can't solve it or can only solve it by guessing.

My initial puzzle:

**9 8** 16*

*** *** ***

2** **9 **8

*4* **7 *83

6** 2*4 **7

87* 3** *9*

5** 7** **4

*** *** ***

*28 **1 3**

This is as far as I get:

**9 8** 16*

*8* *** ***

2** **9 7*8

14* **7 *83

693 284 517

87* 31* 49*

5** 7** *24

*** *** **1

*28 **1 3**

Is there a way of solving it without guessing? I thought guessing was not part of these puzzles.

Any help much appreciated.

Thanks

David