It has been theory for a number of years that "ghostly" manifestations cause a disruption in the ambient electromagnetic fields of a location. Due to this theory investigators have incorporated a wide array of EMF (electro magnetic field) meters as part of their standard equipment. We have proven, based on this previous theory, that areas that appear to be "haunted" do in fact have erratic EM fields. The EMF meter has become the most basic and essential device of an investigators ghost hunting arsenal.
There are a wide variety of meters available on the market ranging in cost from 10 dollars to 600 dollars. You have single axis, double axis, and even triple axis meters for sale. Here is a quick break down of the various meters on the market today.
Single Axis EMF meters read from one direction, usually directly in front of it. These units with have 1 sensor housed in the case. This means you have to be pointing directly at what you are trying to get a reading of to register a hit. If you are using a single axis meter on an investigation an anomaly could be 2 inches above the meter and you would never get a reading if the field were small. Although by turning the meter 90 degrees and face the sensor towards to energy field it will take an accurate reading.
Additionally the sensors could be to the sides or bottom of the meter and you would not register a reading unless the orientation is changed. All EMF meters have to be in the EM field of an anomaly before it will register a reading. The more sensitive the meter the further away from the anomaly you can be before registering a reading.
Double or Dual Axis EMF meters take readings from 2 directions due to fact they have 2 sensors, usually directly in front of the unit and the bottom. Again this will vary from model to model. Like the single axis if this reads from front and bottom if an anomaly is directly above the meter it will not register the actual field strength unless the orientation of the meter is changed.
A triple Axis EMF meter will read from 3 directions, usually from front, bottom, and top. Again this also will vary from model to model and position of the sensors within the unit. Like the others if the anomaly is to the sides where there are no sensors you will not register any deviations unless the orientation of the unit is changed.
Now to the draw back of these meters. All meters have a range of exactly zero feet. This means that all gauss meters, electric field meters, RF/microwave meters, etc. can only measure the strength of the field AT THE LOCATION OF THE METER. What distinguishes one meter from another is the sensitivity. In other words, what is the smallest field strength that the meter can detect? A gauss meter with sensitivity of 0.1 mG is more sensitive than a meter that can only detect down to 1.3 mG. While the meter that is more sensitive can be successfully used further away from the source of the field, it is still only measuring the field at the location of the meter. The closer to the "core" of the anomaly your meter is, the stronger the field reading, as the field strength dissipates rapidly from it's generating source.
Another factor we have to take into consideration with this research is if the meter is a calibrated or non-calibrated meter. A non-calibrated meter reads alternating fields, which means it can read energy at varying Hz rates. A calibrated meter is one designed to read direct currents and it is usually calibrated to read energy cycling at 50 or 60Hz because this is the Hz rating of the power grid in the US. We do not know exactly what the variation of Hz levels these anomalies cycle at as of yet. A lot of times when using a calibrated meter that is set for 50 or 60Hz you will not get a reading on a anomaly if it is cycling at per say 30Hz.
It is best to use both calibrated and non-calibrated meters in your research. If you are using a non-calibrated meter and receive an energy spike you can quickly try to get a reading with the calibrated meter. This will determine immediately if it is a man made field. If the meter which is calibrated at the 50 or 60Hz level gets a reading, it may be a man made field. If you are not getting any readings with a calibrated meter, but the non calibrated meter is spiking then you have a strong case for a anomalous energy field since it is not cycling at 50 or 60Hz as all man made fields do.