Martin/Michael,
Small update to the response.
I figured "scale" may possibly be referring to the meters per degree on the map. If you take 3,000 pixels and divide it by a 4 degree spread, it comes out to 750, while 3,300 pixels divided by a 2.5 degree spread comes out to 1,320.
Maybe the author wanted to introduce a level of inaccuracy to the gauge by rounding to 1,000 and 700?
When Tom and I worked on the LORAN gauge we did some map work, but that was to plot a set of consecutive stationary points instead of a moving map. If you would like, I can go through the code and materials I have and see how he did that and I can get back to you. If it's good with him I can probably recycle the code.
The gauge would not be as in-depth as what Tom was able to work out, but something more simple where you just got a dot or a set of dots on a stationary map or set of maps, depending on the location of the aircraft.
Would you folks be willing to go that type of route instead? It may take a while, but it's another possibility.
I'll look more into the moving map gauge this weekend.
Regards,
Jorge
Miami, FL