Third, TD estimates were compared to OEI estimates in the same compressor operating state. For Solution 1 overights, comparable states were identiable. Solution 2 measured over longer periods, increasing the likelihood that operating state would change during measurements. This type of impact was seen at 3 of 15 facilities. Since operating state changes may have created substantial variations in emissions, the comparison weighted the OEI estimates by the time in each state over the measurement period (SI Section S-2.6). Using a weighted average OEI assumes that total estimate of emissions from Solution 2 eectively averages emissions in a manner similar to the weighted average OEI. The validity of this assumption is impossible to test and is indicative of the challenges of comparing TD estimates to complex time-averaged OEIs in any MII program.