The level of the sun straylight is assessed during the solar eclipse period in
September-October 97. The telescope is pointed to a position on the sky
which has a solar aspect angle of 60 degrees. The absolute sky brightness
is monitored when entering the umbra period and exiting it. Any measurable
difference signal can be attributed to sun strayligth. In order to calibrate
the signal difference absolutely a measurement on a celestial primary 
standard is performed on the same revolution. At 170 micron this is the star
HR6705 (Gamma Dra).