Changes in ratios of simultaneous TSI measurements with the ACRIM3’s Sensor A (primary radiometer) or Sensor B (secondary radiometer) to the least used Sensor C allow tracking of changes due to solar exposure in the two more frequently used sensors. Sensor A has degraded by 1000 ppm over the 13 years on orbit. This degradation is corrected using a 6th order polynomial fit in released TSI values from the instrument (plot from acrim.com).