USING a MASK for estimating the TSYS

-- SET MASK       SET MASK 100-200, BATT=1-4 
                     channels 100 to 200, in spectra type 1 to 4
-- ENA MASK       Enables MASK, necessary after MASK definition
-- DISA MASK      Disables MASK
-- SET DEFMASK    Back to default mask: 5 first and last points
-- SET NOMASK     Deletes the default mask