I picked up a couple of these when they were on sale at a local purveyor of Chinese merchandise. I'm a sucker for a sale. I used them to level a sunken deck. (Really bad construction- no foundation at all.) My 4 and 6 ton didn't work because of the small base. The large base of this was wonderful. I added supports and the deck was level. My next project with these was pushing up a floor where the joists had rotted. There was no sag over a couple of days. Getting the thing to retract was an XX canine; just like some others have noted. I wish I had known this before I got the release valve totally unscrewed.