Would you have preferred that 1-(1/cos(x)*cos(a.t+x) also return 1.1E-14 ? It did in Excel versions prior to Excel97. That is the obscure reference to an "
optimization" in http://support.microsoft.com/kb/78113 Since 97, if the final operation involves taking the difference between numbers that are equal to 15 figures, then Excel will return zero even if their binary ...