for the UK, CAP493 sec 3 chap 3 para 7
IRVR values are to be passed to aircraft at the beginning of each approach for landing and, thereafter, whenever there is a significant change in the RVR until the aircraft have landed. A significant change is defined as a change in value of one increment or more. The current RVR value is also to be passed to aircraft before take-off.
7.2
Even though a pilot may have received an IRVR value from the ATIS broadcast, controllers must ensure that they pass the current value as specified above.
7.3
When all three positions are to be reported to the pilot, they are to be passed as three numbers relating to touchdown, mid-
point and stop end respectively, e.g.
“RVR runway (designator) 650 —500 — 550 metres”.
7.4
If only two values are to be passed, they are to be individually identified, e.g.“RVR runway (designator) Touchdown 650 — Stop End 550 metres”.
7.5
A high degree of priority should be given to such broadcasts to ensure that current RVR information is provided to pilots with the minimum delay.