[Thomas Gaudich]

Hello! I agree that calculating everytime you want to find the value is not practical. Since you have to do it several times using diferent values, your sistem works very well. In my worksheet i use this only one time, with a button associated to a macro in VisualBasic, so i only have to clic the button.
Anyway, i´ve made some 'hand' calculations regarding this two methods to find the 'f' value and i've noticed that your method is more accurate (i'm talking about the fifth decimal place) than with 'normal' goalseek. Regarding this, i've multiplied, by a factor of 1000, my calculations, to make the goalseek more accurate.
regards
thomas