The following program is carried out in order to consolidate the PHT calibration of chopped measurements and derive signal losses due to the high chopper frequency compared to signal stabilization time. - observation of IC5052: chopped measurements plus nodding as a reference. Several filters are taken to have several contrast levels between background and source. The measurement includes staring and chopped observations .HISTORY 23/02/98 JA New version for IC5052 (C100: 60 um) .OTT .TDT