Method for correcting errors of measurement system output, the system comprising a base measurement system BS and a correction system, comprising the steps of: acquiring BS sensor data and providing the BS sensor data to a processing algorithm, storing the BS sensor data associated with a time stamp indicating the time of sensing, calculating BS output values by processing the BS sensor data in the processing algorithm, storing the calculated BS output values with an associated time stamp indicating sensing time of the BS sensor data which are the basis for the calculated BS output values, acquiring correction system sensor data associated with a time stamp indicative of the time of sensing, supplying the BS sensor data, the BS output values and the correction system sensor data with corresponding time stamps to a fusion filter, calculating, by the fusion filter, correction values for correcting constant errors considered not to change during a lag time, by calculating an error between the BS output values and the correction system sensor data having corresponding time stamps, and correction increments (20, 22) for correcting errors caused by processing the BS sensor data containing yet uncorrected constant errors, wherein the correction increments reflect the change of an error in a BS output value over time due to integration and/or summing up BS sensor data in the processing algorithm, applying respective correction values to the BS sensor data and generating recalculated BS output values by processing these corrected BS sensor data by the processing algorithm, applying the correction increments to the recalculated respective BS output values and storing these recalculated BS output values, and outputting the most recent output values of the processing algorithm for further data processing, wherein the latest calculated correction values are stored; and in case that no correction system sensor data with said lag time shorter than a predetermined threshold is available, in the applying step, a correction is performed only on the basis of the stored correction values by applying the stored correction values to the BS sensor data. acquiring BS sensor data and providing the BS sensor data to a processing algorithm, storing the BS sensor data associated with a time stamp indicating the time of sensing, calculating BS output values by processing the BS sensor data in the processing algorithm, storing the calculated BS output values with an associated time stamp indicating sensing time of the BS sensor data which are the basis for the calculated BS output values, acquiring correction system sensor data associated with a time stamp indicative of the time of sensing, supplying the BS sensor data, the BS output values and the correction system sensor data with corresponding time stamps to a fusion filter, calculating, by the fusion filter, correction values for correcting constant errors considered not to change during a lag time, by calculating an error between the BS output values and the correction system sensor data having corresponding time stamps, and correction increments (20, 22) for correcting errors caused by processing the BS sensor data containing yet uncorrected constant errors, wherein the correction increments reflect the change of an error in a BS output value over time due to integration and/or summing up BS sensor data in the processing algorithm, applying respective correction values to the BS sensor data and generating recalculated BS output values by processing these corrected BS sensor data by the processing algorithm, applying the correction increments to the recalculated respective BS output values and storing these recalculated BS output values, and outputting the most recent output values of the processing algorithm for further data processing, wherein the latest calculated correction values are stored; and in case that no correction system sensor data with said lag time shorter than a predetermined threshold is available, in the applying step, a correction is performed only on the basis of the stored correction values by applying the stored correction values to the BS sensor data.