The other alternative is to be a bit remote from New River. In that case, the mine outgrew it's original location, so New River was built where there was more space to be had. Coal seams can be spread out, so mines may well move at some point in time. Or, a new location may not necessarily mean the old seam is played out. All a possibility.

Anyway, I found the formula:

>>>> Maybe it's time for a discussion of selective compression for

>>>> those as yet unfamiliar with it. This is a concept that was

>>>> developed AFAIK by the RPI club. An exponential curve is

>>>> used to transform prototype numbers of cars to the model. It

>>>> would be something like:

>

>>

>> proto model Exponential .7

>> cars cars

>> 1 1 1

>> 2 2 2

>> 3 2 2

>> 4 3 3

>> 5 4 3

>> 10 5 5

>> 20 8 8

>> 50 18 15

>> 100 25 25

>>>>A scheme like this keeps everything in resonable proportions while

>>>>avoiding excessive numbers of cars. Dos anyone know the mathematical

>>>>formula - JP ?

> Yep, I guesseed it to be an exponential decay and my trusty HP48G

> says a good fit is to use the prototype number of cars to the .7 power.

> It gives the third column.

Kennedy