For more than 4 years we puzzled with 4000 thousand shards of a 2 by 3 meter glass plate on which you can see an etched map. This map was created by the German Night Fighter commanders used to intercept the Allied bomber formations. The official name is 'Gradnetz' or 'Gradnetzmeldeverfahren'. This system was already in use, before the war and stayed in use, without major changes until April 1943. Because this system was easy to understand for the allies they had to modify it. The result was the introduction of the 'Jagdtrapez' by the head of the Air Force Intelligence, General Ln-Truppe Martini.
The project will ultimately yield a nearly complete glass map that is unique in the world.
Many hundreds of man hours and puzzling 4 years later, we have now started the final stretch. A final period of excavations were started and yielded, sometimes to our surprise, still valuable pieces..
Below is our main weapon in the fight against complete despair. A short theory: When a glass plate is rolled into a flat sheet, it is still hot and therefore (although invisible to the naked eye) still a little bit fluid. This also means that there must be (very) minimal differences in the thickness.
ALL, more than 4000 pieces are now measured for thickness with a micrometer, and there is indeed a pattern. These are printed in colors. The puzzle is a lot easier. You can than measure the thickness of a shard and you can compare it to the color chart and see where it belongs. A bit more accurate than: SOMEWHERE on 3 by 2 meters.
With the help of special glue, which cures by UV light large plaice are made. Not the whole plate is glued, because it is in the attic and ONE DAY it has to come down the stairs.