The purpose of the DIMM is to inform the visiting astronomer about the imaging quality of the night, so as to help him scheduling his observation sequence in the most efficient way.
The seeing is measured not more than 30 degree from zenith on bright stars with the differential centroiding method [The E.S.O Differential Image Motion Monitor ; Astron. Astrophys. 227, 294-300 (1990) (ps file without figures) ]. The seeing is corrected from airmass and computed for an equivalent long exposure at 0.5 microm. The accuracy is better than 10% down to 0.2 arcsec (see a record low at La Silla).
