Glass board (cartography)
The glass sheet is a tool for semi-graphical calculation of areas of maps and map . It was used, for example, in the Baden state survey to determine the official property area. There were versions for the scales 1: 500, 1: 1000, 1: 1500 and 1: 2500.
application
The glass panel is a 14 × 24 cm large glass plate on which parallel lines are engraved at the same distance . It was made for calculations in different scales. With the glass board you can quickly read the height of double triangles. To do this, place the glass panel parallel to a line measured in nature, place a ruler perpendicular to it and move the glass panel so that one point of the double triangle rests on a line. Read the other tip of the double triangle and estimate the rest.
The values determined were entered in the so-called protocol of the Baden state survey. The areas were calculated using two different approaches and the results then averaged. These areas were compared to larger calculated blocks and counted as the officially determined areas of the properties.
Error theory
The area calculation with the glass sheet achieves fairly accurate results because the area of a triangle is calculated from the base × height / 2. Because the base side is a dimension measured in nature that has centimeter accuracy, the error is relatively small when using the smallest possible base side and the greatest possible height.