Fit windows

 
Generally all data shown after a display command are considered by a fit.
With the command FWIN parts of the data may be selected
either by cursor or terminal prompting loop defining the actual fit regions.
Fit windows may extend beyond the displayed spectrum segment.
However, only data within the display region are fitted.
Note that unless  explicitly demanded within the command FIT,
data points less or equal zero are not included by the fit.