The paper presents an updated analysis of the Cosmic Microwave Background (CMB) spectrum using data from the Far Infrared Absolute Spectrophotometer (FIRAS) on board the Cosmic Background Explorer (COBE) satellite. The authors refine the calibration and analysis of the FIRAS data, providing tighter upper limits on deviations from a blackbody spectrum. Key results include: - The RMS deviations from a blackbody spectrum are less than 50 parts per million of the peak CMBR. - The Comptonization parameter \( |y| \) is less than \( 15 \times 10^{-6} \) and the chemical potential \( |\mu| \) is less than \( 9 \times 10^{-5} \) (95% confidence level). - The absolute temperature of the CMBR is determined to be \( 2.728 \pm 0.004 \) K (95% confidence level). - The dipole direction is found to be \( (\ell, b) = (264.14^\circ \pm 0.15, 48.26^\circ \pm 0.15) \) (95% confidence level). The analysis also includes improvements in the calibration process, such as correcting biases in pixel data, borrowing data from neighboring pixels, and using a larger number of points in the spectrum. The results are consistent with previous findings and provide stringent constraints on theories of the early universe and cosmic structure formation.The paper presents an updated analysis of the Cosmic Microwave Background (CMB) spectrum using data from the Far Infrared Absolute Spectrophotometer (FIRAS) on board the Cosmic Background Explorer (COBE) satellite. The authors refine the calibration and analysis of the FIRAS data, providing tighter upper limits on deviations from a blackbody spectrum. Key results include: - The RMS deviations from a blackbody spectrum are less than 50 parts per million of the peak CMBR. - The Comptonization parameter \( |y| \) is less than \( 15 \times 10^{-6} \) and the chemical potential \( |\mu| \) is less than \( 9 \times 10^{-5} \) (95% confidence level). - The absolute temperature of the CMBR is determined to be \( 2.728 \pm 0.004 \) K (95% confidence level). - The dipole direction is found to be \( (\ell, b) = (264.14^\circ \pm 0.15, 48.26^\circ \pm 0.15) \) (95% confidence level). The analysis also includes improvements in the calibration process, such as correcting biases in pixel data, borrowing data from neighboring pixels, and using a larger number of points in the spectrum. The results are consistent with previous findings and provide stringent constraints on theories of the early universe and cosmic structure formation.