Osborne Fire Finder - Use of The Fire Finder

Use of The Fire Finder

The system is composed of a topographic map of the area oriented and centered on a horizontal table with a circular rim graduated in degrees (and fractions). Two sighting apertures are mounted above the map on opposite sides of the ring and slide around the arc.

The device is used by moving the sights until the observer can peek through the nearer sighting hole and view the cross hairs in the further sight aligned with the fire. The fire lookout notes the degrees on the graduated ring beneath the sight. The original Fire Finder was capable of a crude estimate of elevation based upon the level and elevation of the table, calculating distance and rough position of the fire by reference to any distinctive terrain features and by use of the scale shown on the map. However, in actual practice, fire distance and location were normally established using two or more Fire Finder-equipped towers, using the intersection method to fix the precise location of the fire. Dispatchers at a central facility used a compass rose to mark lines of position from each reporting tower onto a large map to quickly find where the reported bearings intersect.

Today, a more precise determination of a fire location can be made by the use of a single Fire Finder in conjunction with a digital elevation model (DEM).