D and X
Sounds pretty much like the HS125 data also. A quaint English way of performance calculation methinks?
We certainly have the 'D' value charts, yet rarely have to resort to them. For the vast majority of performance planning a quick reference table gives us a value for required runway length without concern for the effect of clearway, stopway, slope, wind etc. This gives us a runway length more than adequate with lots spare room. After all most runways are more than long enough, certainly for us.
But if we need to make more accurate calculations using all the TODA TORA clearway stopway information then we go into the 'D' calcs using all the data available.
Quick reference table might give 5500', using 'D' charts could bring it down closer to 4500'.
Sycamore has put given you an academic answer, mine is just to add that indeed they are still a consideration for take off calculations should we be performance limited.
Hope this helps.