Program COFECHA is a new computer program developed to improve the quality control of tree-ring data by identifying potential errors in crossdating and measurement. It addresses limitations of existing methods by not requiring a known error-free series, allowing for the presence of locally absent or double rings, testing multiple series simultaneously, and examining individual segments rather than the entire series. The program filters data with a cubic spline to remove low-frequency variance, applies a log transformation to enhance small ring variability, and computes a master dating series as the mean of all filtered and transformed series. Each series is then tested against the master series, calculating correlations for segments of the series at various positions. The program identifies segments with low or inconsistent correlations, indicating possible errors in dating or measurement. It also flags statistical outliers and provides a detailed output for each segment, including correlation values, positions of high correlation, and potential dating errors. Program COFECHA is designed to complement visual crossdating by providing an independent tool for verifying the accuracy of dating and measurement. It has been successfully used in various regions, including California and Argentina, for data quality control in developing chronologies. The program's output includes six parts, each providing different aspects of the data analysis, such as correlation values, segment statistics, and identification of potential errors. The program is particularly useful for identifying crossdating errors, measurement errors, and growth disturbances in trees. It is recommended for use in conjunction with visual crossdating and other quality control methods to ensure accurate and reliable tree-ring data.Program COFECHA is a new computer program developed to improve the quality control of tree-ring data by identifying potential errors in crossdating and measurement. It addresses limitations of existing methods by not requiring a known error-free series, allowing for the presence of locally absent or double rings, testing multiple series simultaneously, and examining individual segments rather than the entire series. The program filters data with a cubic spline to remove low-frequency variance, applies a log transformation to enhance small ring variability, and computes a master dating series as the mean of all filtered and transformed series. Each series is then tested against the master series, calculating correlations for segments of the series at various positions. The program identifies segments with low or inconsistent correlations, indicating possible errors in dating or measurement. It also flags statistical outliers and provides a detailed output for each segment, including correlation values, positions of high correlation, and potential dating errors. Program COFECHA is designed to complement visual crossdating by providing an independent tool for verifying the accuracy of dating and measurement. It has been successfully used in various regions, including California and Argentina, for data quality control in developing chronologies. The program's output includes six parts, each providing different aspects of the data analysis, such as correlation values, segment statistics, and identification of potential errors. The program is particularly useful for identifying crossdating errors, measurement errors, and growth disturbances in trees. It is recommended for use in conjunction with visual crossdating and other quality control methods to ensure accurate and reliable tree-ring data.