The radio spectra measurement points are appoximated by curve for the calculation of spectral parameters (radio emission power, spectral index and others). Least squared method is used for approximation of the spectral data.

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Curve range sets the frequency interval in which a curve is drawn.

Curve type defines the next approximational dependencies:
Linear:                  

Parabolic:                  

Linear + exp(+x):    

Linear + exp(-x):    

The best curve   is a curve with one of the above types that has the minimum deviation from the measurement points of the spectrum.

SpInd=const on curve edges: The fitting curve is divided to three parts. The middle part between utmost measurement points has selected curve type. Two external parts of curve have const spectral indexes equal to spectral indexes calculated in the extreme measurement point on the left/right.

Weights for Fluxes:
Equal: All weights are given equal.
Case A: All weights are inverse proportional to the flux errors.
Case B: All weights are inverse proportional of the squares to the flux errors.

Considerably different frequencies: The spectral approximation can be incorrect for a small number of the points, the frequenly of which are very close. If the frequencies differ less than the quarter of the decade these spectra points can be considered as indistinguishable. The button being switched on, such points are examined as one when you choose the curve type.

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All undeleted points are used for fitting (even if out of curve range).

The line with SpInd=0.8 is used as default approximation for only one measurement point.