The article by GUNTHER SAUERBREY discusses the use of quartz crystals for weighing thin layers and micro weighing. When a foreign layer is placed on a quartz plate excited at its natural frequency, the plate's natural frequency changes due to an increase in the mass. This frequency change can be precisely measured, making it a highly sensitive method for weighing thin layers. The mass density and frequency change are proportional, and the proportionality constant can be derived from the natural frequency of the quartz crystal, eliminating the need for empirical calibration. The accuracy of the layer weighing method is primarily limited by the temperature dependence of the quartz frequency, which is about ±4·10⁻⁹ g·cm⁻² over a 1°C temperature range, corresponding to a mean thickness of 0.4 Å for a density of 1 g·cm⁻³. This method has also been used for direct weighing (micro weighing), achieving a precision of 10⁻¹⁰ g. The article outlines the problem of determining the thickness of thin layers, which is crucial for many experimental studies. Traditional methods often rely on the mass of the layer, but for thin layers, the true area and macroscopic density are often unknown. The method described uses the natural frequency of a quartz plate excited at its natural frequency to measure the mass density and thickness of thin layers. The influence of foreign layers on the natural frequency of these plates is investigated to determine their suitability for weighing thin layers. The natural frequency of a quartz plate depends on its thickness and the thickness of any foreign layers on its surface, making quartz plates suitable for this purpose.The article by GUNTHER SAUERBREY discusses the use of quartz crystals for weighing thin layers and micro weighing. When a foreign layer is placed on a quartz plate excited at its natural frequency, the plate's natural frequency changes due to an increase in the mass. This frequency change can be precisely measured, making it a highly sensitive method for weighing thin layers. The mass density and frequency change are proportional, and the proportionality constant can be derived from the natural frequency of the quartz crystal, eliminating the need for empirical calibration. The accuracy of the layer weighing method is primarily limited by the temperature dependence of the quartz frequency, which is about ±4·10⁻⁹ g·cm⁻² over a 1°C temperature range, corresponding to a mean thickness of 0.4 Å for a density of 1 g·cm⁻³. This method has also been used for direct weighing (micro weighing), achieving a precision of 10⁻¹⁰ g. The article outlines the problem of determining the thickness of thin layers, which is crucial for many experimental studies. Traditional methods often rely on the mass of the layer, but for thin layers, the true area and macroscopic density are often unknown. The method described uses the natural frequency of a quartz plate excited at its natural frequency to measure the mass density and thickness of thin layers. The influence of foreign layers on the natural frequency of these plates is investigated to determine their suitability for weighing thin layers. The natural frequency of a quartz plate depends on its thickness and the thickness of any foreign layers on its surface, making quartz plates suitable for this purpose.