Declaration: TSpdc.BLMode: TBLMode;
The property BLMode specifies the type of the baseline applied to the spectral descriptor:
blNone ... no baseline is subtracted
blLinear ... the baseline is a line controlled by the parameters ParB1 and ParB2
blP1Level ... the baseline is a constant level controlled by the parameter ParB1

Please see the predefined spectral descriptors for a detailed explanation of the various types of descriptors.