While the outline of Germany is the contemporary one the map of the Harz shows the railroads pre WW II. Three different companies formed a network of metre gauge railroads (brown outline), the only ones that traversed the mountains. The BAE (red outline) is a logical free lanced addition to that network.
Meter gauge used to be the so common in continental Europe that the French apply the word narrow gauge only to gauges inferior to one meter. While most narrow gauge lines were independent connections between two standard gauge lines there were also some real networks. One of them was the network in the Harz mountains formed by the lines of three independent companies, the NWE, the GHE and the SHE. Two of them do exist even today as tourist attraction and are chiefly steam operated. My favorite railroad to model would have been just the one that has disappeared (SHE) but as I prefer prototype freelancing to pure prototype modeling I invented a fourth company connecting with the other ones. This was the birth of the BAE.
It had come to my attention that the two major holiday resorts in the upper Harz mountains, Braunlage and St.Andreasberg, had never been connected by rail. While the distance is only four miles there is a gulch 300 ft. deep between them*. A bridge or viaduct that high and half a mile long would have to be built. Impossible. That’s why I drew the mainline as a big upside down U contouring the gulch to the north. (see map below) Some years later the company built a branch line to Sieber, which turned out to have much heavier traffic than the original line and became the real main. This way the line from the junction Sonnenberg (highest point on the system) to St. Andreasberg became a mere branch but the original name of the company Braunlage-Andreasberger-Eisenbahn (BAE) persisted.
I wanted to model both lines, the main and the branch and copy the direction and percentage of the grades in a convincing way. Ah, before I forget: I invented another branch, a mine branch owned by the mining company, that was to be modeled, too.
Meter gauge (about 3 1/2') in 1:45 proportion (0 scale in central Europe) is 22.2 millimeters. This gauge is called 0m.