The paper presents a room-temperature, carbon nanotube-based nanomechanical resonator with atomic mass resolution. The device, which functions as a mass spectrometer, has a mass sensitivity of 1.3×10^-25 kg/√Hz, equivalent to 0.40 gold atoms/√Hz. This extreme sensitivity allows for the observation of atomic mass shot noise, similar to electronic shot noise measured in semiconductor experiments. Unlike traditional mass spectrometers, this nanomechanical device does not require the destructive ionization of the test sample and is more sensitive to large molecules, making it potentially suitable for chip integration. The resonator's mass sensitivity is achieved through the use of carbon nanotubes, which are naturally smaller and less dense than standard resonators, reducing their mass to approximately 10^-21 kg. The geometry of the nanotube, specifically its length and diameter, is crucial for maximizing the responsivity, which is the ratio of the shift in resonant frequency to the change in mass. Singly clamped geometries are preferred due to their higher quality factors and increased dynamic range. The experimental setup involves evaporating gold atoms onto the nanotube and measuring the resulting frequency shift using a nanotube radio receiver design. The frequency shifts are analyzed to determine the mass of adsorbed atoms, either through atomic mass shot noise or the statistical distribution of frequency shifts. The results demonstrate that the device can accurately measure the mass of gold atoms, with a measured atomic mass shot noise of 0.014±0.002 MHz²/s²/Hz, corresponding to an atomic mass of 0.29±0.05 zg, consistent with the accepted mass of gold. The nanomechanical mass spectrometer offers significant advantages over traditional mass spectrometers, including the ability to handle large biomolecules without ionization, higher sensitivity at higher mass ranges, and compactness, making it a promising tool for future applications.The paper presents a room-temperature, carbon nanotube-based nanomechanical resonator with atomic mass resolution. The device, which functions as a mass spectrometer, has a mass sensitivity of 1.3×10^-25 kg/√Hz, equivalent to 0.40 gold atoms/√Hz. This extreme sensitivity allows for the observation of atomic mass shot noise, similar to electronic shot noise measured in semiconductor experiments. Unlike traditional mass spectrometers, this nanomechanical device does not require the destructive ionization of the test sample and is more sensitive to large molecules, making it potentially suitable for chip integration. The resonator's mass sensitivity is achieved through the use of carbon nanotubes, which are naturally smaller and less dense than standard resonators, reducing their mass to approximately 10^-21 kg. The geometry of the nanotube, specifically its length and diameter, is crucial for maximizing the responsivity, which is the ratio of the shift in resonant frequency to the change in mass. Singly clamped geometries are preferred due to their higher quality factors and increased dynamic range. The experimental setup involves evaporating gold atoms onto the nanotube and measuring the resulting frequency shift using a nanotube radio receiver design. The frequency shifts are analyzed to determine the mass of adsorbed atoms, either through atomic mass shot noise or the statistical distribution of frequency shifts. The results demonstrate that the device can accurately measure the mass of gold atoms, with a measured atomic mass shot noise of 0.014±0.002 MHz²/s²/Hz, corresponding to an atomic mass of 0.29±0.05 zg, consistent with the accepted mass of gold. The nanomechanical mass spectrometer offers significant advantages over traditional mass spectrometers, including the ability to handle large biomolecules without ionization, higher sensitivity at higher mass ranges, and compactness, making it a promising tool for future applications.