Last week I printed 12 grids from the times website (3 each of easy, mild, difficult and fiendish)

and I noticed that the difficulty in each case was exactly the same and you only needed the same techniques to solve each type.

Now knowing this does that spoil the puzzle because if you get stuck say early on you know you may have done something wrong because you can not solve it using only the techniques you know you need?

THE NEXT BIT MAY BE CONSIDERED A SPOILER

easy - no need for candidates, every cell can be solved directly.

mild - if no direct solution for a cell then it had 2 or at the most 3 candidates at the most. Eventually you get to the point that solving one square gives you the rest.

difficlt - after the inital cells you can get with ease (usually about 10) each cell has at least 3 candidates but eventualy you will spot a pair or tripple that reduces the candidates in some rows or columns producing more pairs / triples and so on until you get that cell that makes the puzzle collapse

fiendish - same as difficuly but before you get that first pair / tripple you have to do a little look ahead logic to reduce the candidates in a few cells to create that initial pair / tripple. i.e. working out that the middle three cells of a box can not or must contain a certain number. This may only reduce the candidates in say 3 other cells but that is enough to get going.