U

 U.C.C. § 3-104(a) provides: 'Except as provided in subsections (c) and (d), 'negotiable instrument' means an unconditional promise or order to pay a fixed amount of money, with or without interest or other charges described in the promise or order . . . .'  

The principal amount must be fixed. 'A fixed amount is an absolute requisite to negotiability.'  This is because unless a purchaser can determine how much it will be paid under the instrument, it will be unable to determine a fair price to pay for it, which defeats the basic purpose for negotiable instruments. To ...