Over an hour to figure this one out...... ....... do not want to see one of these again.......I thought if you got a bonus, it was a reward of sorts.......but then the only "0" puzzle I can usually solve is the 3 t0 -3....(the other "0" puzzles usually take over 1/2 hr to do if I do get them).......so why would this 3 to -2 prove so difficult for me?

I think it's the asymmetrical nature of the puzzle that makes it so difficult. The puzzles I struggled with most on Advanced Puzzles IV were 9x9 puzzles going from -1 to +7. One of these in particular was the last puzzle solved by several people.

Just finished another one of these where 13 cells were zeroes plus one cell with a given zero.....so on a 36 cell grid more than a third were zeroes....this time it "only" took 27 minutes

I presume you mean 13 cages, not 13 cells! Sounds quite mind boggling!

No, 1 cage had 4 zeroes and 3 other cages had 3 zeroes in each and then there was singleton zero!

Now I'm totally confused! Surely the 6x6 puzzle would have 6 of each number from -2 up to 3?

I think the zero is the solution for the cage, note one of the cells within the cage. 0- 0x 0/

yes all the numbers end up being present but when you have a cage that is marked X and 4 zeroes, and another cage marked X and 3 zeroes and yet another cage marked X and 3 zeroes, and then there was a 3 cell cage with / , plus one cell with a zero which is no where near the other zeroes, then you cannot even use it to determine where each zero goes in each lie of numbers.....so then you are left trying various combinations in trying to use the other numbers.......there was one cage (3 cells) marked with a -3 and there were a number of combinations that worked but did not help in deciding where the rest of the numbers should go!!!!!

So probably the zeroes are the candidate numbers? (so 13 cells have a "zero" guess in them?)

yes