I had a phone interview. People asked me how to get the frequency of microwave oven if I do not know. I said measure it. They said, you are not allowed to use any measurement tools. Then I said, read product spec. They said, no, you do not have the spec. Finally I said I do not know. I think they are asking me something related to eddy current according to the questions after that. Back to my original question, anybody knows the answer? Thanks.