The determination of Particle Size Distribution (PSD) is one of the most important fundamental physical properties of soils, which determines both the physical, chemical, mechanical, geotechnical, moreover environmental behavior. Although the measurement of PSD is continuously performed in soil labs using different techniques there are two important problems not solved: automation and continuous PSD curve generation. To overcome the mentioned troubles there are various sensors based on different physical principles and new data storing methods to measure the density-time function of settling soil suspensions. In this paper we introduce one possible device for measurement and storing of the density changes versus time. The equipment has a form of a real areometer widely used in many fields of the life (determination of sugar content of must or alcohol content of distilled spirits, etc.) The device equipped with patent pended capacitive sensors on the neck of the areometer, which can measure the changes of water levels nearby the neck of the areometer in 1 µm precision with less than 10 µm errors. The typical water level change nearby the sensor during the measurements is 3-5 cm, which makes possible a very accurate determination of density changes. The measured signals are stored in the memory of equipment and after the termination of the measurement the database is downloaded to the to a PC via a modified USB-serial port. Data evaluation using a new evaluation method can be carried out online or using a saved file later at any time. The big number of measured data points led to the introduction of a new evaluation method, the Method of FInite Tangents or shortly: the “FIT method”. Because the whole system can be managed as the superposition of many mono-disperse systems, it is possible to divide the measured density-time function into grain-size fractions with tangent lines drawn to finite but optional points. For calculating the settling speed of given fraction, this tangent lines are useable, because the gradient of density changes is equal to the product of settling speed and mass of given fraction. The settling speed of all fractions is calculable using the Stokes law, so thus the mass of all floating fraction is calculable. Because the soil-suspension is a poly-disperse system, the measured density increments can be considered as an integration of finite mono-disperse systems, which mean that it can be interpreted as the sum of linear density vs. time functions. If the mass of all grain-size fractions are known, the particle size distribution can be calculated easily. For the FIT-method is relatively easy to write the computer code, where the intervals of grain-size fractions are freely adjustable, so using this program, almost all particle size distribution systems can be determined, not only the uniform distribution. Using an appropriate controller and calculating program, the particle size distribution can be calculated immediately after downloading the measured data or anywhen later. It is also possible to make calculations from one dataset using different PSD systems. The use of this technique needs the same sample preparation as the past methods. The automated reading requires less manpower to perform the measurement--which also reduces human error sources--and makes easy to perform parallel measurements, but also provides very detailed PSD data that has advantages like revealing multi-modality in the particle-size distribution--among others.