What's relevant is your value in the market, and how much the employer wants you compared to other candidates and their respective salary expectations. It's important to give them the feeling that you are entirely confident in being able to go elsewhere if the deal's not right. Bear in mind also that you can always buy some time to 'think about it' whatever they offer you. Time will generally work in your favour if they want you. They will worry that they'll lose you, perhaps even to a competitor, and so will be more likely to increase their offer, and to justify some extra budget if required.
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Ig Nobel Prize winners
Sun Myung Moon