## 2 Materials and Methods
### Possibilities of the Kappametry Method in Observatory Installation Practice  
From the point of view of problems associated with observatory magnetic observations, the measurement of the magnetic susceptibility of substances is of great importance. The need for susceptibility measurements arises already at the stage of searching for the most suitable place for a magnetic observatory. Strongly magnetic rocks can produce magnetic anomalies that affect the local intensity and direction of the Earth's magnetic field. Such effects can lead to the distortion of magnetometer data [6], requiring additional processing for correcting the influence of anomalies of geological origin. In addition to checking possible intense natural magnetic anomalies, it is also important to take into account the magnetic properties of building materials. This is required to make sure that building blocks, structures, fillers, and fasteners do not contain magnetic impurities. Otherwise, residual magnetization can cause local gradients of several nT/m in the magnetic field. This is critical for the zone in the absolute pavilion where absolute measurements are made. In this zone, the vertical and horizontal gradients of the magnetic field should, if possible, not exceed 1 nT/m [3]. The absolute measurement process includes measurements at 8 different positions for the DI sensor orientation with respect to the East, West, North, and South, and any local gradient in the vicinity of the sensor will inevitably cause spatial differences in the DI magnetometer measurements, making them inconvenient.  
Moreover, a structure made of initially non-magnetic material may acquire undesirable magnetizations due to ferrimagnetic contaminations. This can happen if contaminants, including iron filings, are left over after manufacturing and processing with steel tools. Finally, contaminated concrete can acquire a magnetization during solidification, as shown in Section 3.1.2.  
Nowadays, there are various modern composite materials that can be used for the construction of magnetic observatories. These materials are able to provide necessary reliability and durability if used for the construction of the frames and walls of pavilions, thermal insulation, and even the construction of pillars. Wood is the most widespread non-magnetic material used for the construction of pavilions. Both exteriors and interiors of wooden buildings should be protected from wearing out. Exterior wood is often under attack from weather impacts (temperature variations, moisture, etc.) and, therefore, should be protected with weatherproof paint. Interiors also should be protected, as they may also be subject to wear during use. The same applies to wooden pillars, which are still used in some magnetic observatories. Another material used for pillar construction is marble. However, marble is rather expensive. A cheaper alternative for pillar construction uses glass blocks joined with glue. This construction has been used at many Russianobservatories, such as Paratunka (IAGA code PET) or Klimovskaya (IAGA code KLI) [5]. Nevertheless, the footing for pillars should be concrete.  
There is a way to estimate the magnetic anomaly of a magnetized body by its magnetic susceptibility, mass, density, and distance from it [3]. However, this estimation is approximate, as it assumes magnetically homogeneous objects, whereas real physical bodies can contain different amounts of ferromagnetic particles. Therefore, instrumental determinations of magnetic susceptibility should be an obligatory procedure during the stage of selection of construction materials for a magnetic observatory.