An Athrometer is a very rare technology, developed in the Victorian Era on Earth but perfected in the late 20th century. The device uses Videns Autem Magia crystals placed within the mechanics, the electricity produced is turned into mechanical energy through the clever use of distinct materials which expand and contract when micro-voltage of applied from the crystals. The device is then carefully calibrated so that it can provide reliable strength and approximate bearing of source. Dials and adjustments on the device allow for it to be calibrated and adjusted to focus on detecting specific kinds of non-conventional energy and the types of patterns they create.
Construction
The devices are constructed largely by hand and have never been mass produced. The construction methods were taught to very few groups over time, starting with the device's invention in Victorian London to serve the purposes of a group of investigators of strange occurrences in the city. The design was then passed down and taught to people as needed, the original group which designed it taught many others in many countries how to construction the items and thus many variations exist for various secret societies and police and law enforcement forces throughout the world.
Rarity in the 21st Century
The devices are not very common in the contemporary time periods of 20th and 21st century but are not so rare that they do not exist or are unknown to groups who are serious about investigation of strange occurrences. However, it requires unique knowledge to build one, such knowledge must be gained from one of the groups or organizations (or individuals) who already has it, the designs are unpublished and several groups work hard to keep it that way. Hand written and drawn designs do exist and can be obtained, largely on the black market for large sums of money.
Rarity in the 24th Century
By the 24th century most of the knowledge required to construct these devices has been lost to time over multiple wars, though some of the devices still exist. Similar devices have been constructed, in a crude sense, using similar ideas. However, these devices when properly used can be even more precise than their 24th century equivalents. As such the devices are exceptionally rare in the 24th centuries, mostly in collections and museums where their original purpose is unknown.