Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Calphalon not for smooth top ranges

I purchased this set when it was a 10 pc set. I e-mailed calphalon direct and asked if it would stay flat on the bottom for use on a glass top stove, and the answer was that it would. However, the first time I used the pans (not exceeding reccommended heat settings), they became round on the bottom and only contact the cooking surface in a small spot in the middle of the pan, which of course does not cook evenly. Now I have had this problem with other cheaper brands of cookware also, but thought that a good brand would be better. I would have been a lot of money ahead if I had a bought a cheaper set. It certainly couldn't have performed any worse. I suppose they would replace it, but what good would that do if the new ones are going to do the same thing when they are used?I also find it very difficult to clean.