Good point Stewart, another thing to bear in mind when using a trolley Jack is that the surface the Jack is on should be flat and smooth with nothing like bits of gravel etc to stop it rolling freely as the Jack rises up. If the Jack can't roll in in under the car as it rises then the position of the Jack on the on the spot you placed it on the car will change, with the potentitial for a great deal of expensive damage at the least.
I always sweep the garage floor clear around the trolley Jack before using it, never use it on a carpet, and if I can't find a smooth spot where I am jacking I put down some heavy ply for it to sit on.
Cheers John
