It means you need to weld with it. It will be somewhat difficult for an inexperienced welder to know what 'most happy' looks, feels, and sounds like, but an experienced welder knows the disposition of each machine in his perview, and if handed the business end without knowing what supply is at the other, he will be able to tell YOU which one you've connected to him, AND wether or not you've used extension cables, or set it properly, or have insufficient gas flow, wrong wire tip, a bad connection in the ground terminal. It's like being blindfolded in a room and having a half-dozen teenagers talking to you- you know who's who by what they say, and how they sound... and you can tell by the smell, who showered after gym class, and who sat in the bleachers.
Set it to the lowest, mid-range, and highest point you think you'd spend the most time welding with it, and work with it a bit. Then work around the range and see if you can notice a difference in performance at upper or lower end. If so, remove or add a little capacitance, and try again, see how it affects performance. I've found that for the most part, welding transformers will be happy once you're in the general ballpark, and if any adjustment is required, it doesn't take more than two tries to get it where it's nice across the entire range with just one value.
For all that use my conversion- If you want to thank me, do it in a way that pays forward- Once you've figured out what it likes the most, please post the make and model, wiring diagram, and the capacitance you've found suits best overall, so that others faced with same question find your answers, rather than coming straight to me.
As much as I enjoy helping people, I dislike re-inventing the wheel, and my wife has lots of projects in my bucket-list... so I just can't get on here as much as I used to. My hope was that each time someone worked out the details of a new machine, they'd post a diagram, and the values, and a report of the results, somewhere that a web-search would quickly find it... because someday I won't be around to provide guidance. I lit a torch, and placed it up high enough to illuminate part of the world, with the intention that others would see, light their own from it, and carry it onward.