In addition to the previous answers, and something which I commonly come across is that the mid-point is a minimum of 125, and is dependent on the facilities at the airfield, and theirs/state limits. The mid-point RVR requirement is the take-off minima for that runway, so if TO minima is 150m, then the mid-point landing minima, and the stop-end minima are 150m if you're going to use the stop-end as part of your landing roll-out, if not then it's 75m for taxiing.