If we're talking about an ILS, then the aircraft is flying a steady 3º slope towards the runway, so the slant visibility will be steady all the way down, n'est Pas?
Admittedly it won't necessarily match the visibility
along the runway ...
The minima for this Cat 1 ILS is 776' height above terrain. Descent angle is 3.17º, threshold crossing height is 56' (displaced threshold), so minima is (776-56=) 720' above threshold.
720/tan(3.17º) = 720 / 0.0553834597 = 13 000.2713 feet = 3 962 metres
400m meters for standard lights, and you need 3600 meters vis to become visual at the cat 1 minima
750m for the High Intensity Approach Lighting System, and you need 2850m to be visual with the lights at the Cat 1 minima.
It seems inconsistent with Appendix 1 (new) to OPS 1.430 which requires no increment to DH with ALS out and a 2400 m max RVR/CMV for an ILS approach in any case.
There
is no increment to DH, only to the required visibility - and the RVRs listed in the chart are system
minimums - thus "2400m" is the largest value on the chart, but it isn't the "maximum" allowed - it's the largest "minimum" value allowed