In this guide, I will refer to the combination of HQ Tinker's Calm and HQ Bacon Broth as Tinker's Bacon.
If you have HQ Tinker's Calm and HQ Bacon Broth, an item 34 rlvls higher than your d Skill will be desynthable with a 2.5% chance of success.
If the item is meldable, and you penta-melded it AND used HQ Tinker's Calm and HQ Bacon Broth, you could attempt to desynth it when your d Skill was 44 points below the item's rlvl, but your success rate would be 2.5%.
Currently, as of patch 2.5, there are only two items in the game that provide Careful Desynthesis: Bacon Broth (a meal, 4* CUL) and Tinker's Calm (a medicine, 4* ALC).
NQ Bacon Broth provides Careful Desynthesis 1 (HQ Bacon Broth provides 2) and lasts 30 minutes.
The difference between your desynthesis skill level and the item's "rlvl" determine how much experience a successful desynthesis will give you . You could get 0.30 from an item one time, and then try again without leveling up and get 0.70 from the same item at the same level.
Generally speaking, the less of a chance you have at succeeding, the more experience you will get if you do.
An item's ilvl and jlvl both have no bearing on desynthesis.
The Craft Level (clvl, or c#, followed by 0 or more *s) denotes how hard an item is to craft.
This flvl is the level listed next to the fish in the Fish Guide.
In general, it's the same as clvl for crafters (the level next to the recipe), but with exceptions at 50**, 50***, 51, and 60*.