Different versions of the SET are available. You must use the version applicable for the year in which the flight was operated. Version 5.13 is to be used for flights operated in 2023.
The 2023 version of the SET was improved by updating the aircraft emission models based on the collected samples, switching some aircraft types to actual fuel burn modelling, and including aircraft types which started operating in 2023.
The underlying equation in the SET can be obtained by submitting a request using the contact form (the SET equations are subject to a specific data usage agreement).