You cannot use the CMV to convert any metereological visibility giving you a CMV value lower than 800m nevertheless CMV cannot be use for Take.
"Straight-in approach minima are often expressed in terms of RVR. Following widely used procedures, many airline operators convert the reported meteorological visibility into an equivalent RVR value, called CMV. This conversion is applied by the pilot only for landing, when the required RVR minimum is equal or above 800 m (1/2 sm) and when the RVR is not available (a reported RVR above its 2000 m limit is considered as being not available)."
I hope this can help.
Last edited by mauro.villani; 4th Jan 2017 at 01:53.