It's all done by the excell sheet, so I don't know. But it's 3 separate but identical readings at each gravity. The correction factor is the same at each gravity. Different at different gravities, I don't claim to know why, but that IS why it takes readings at different gravities to come up with the average. I'm not at all freaked out about it because it works, according to people far smarter than me. Sean Terril, if I recall correctly, is a nuke tech.
Trust, but verify. I'll try it out and compare with hydrometer samples.
FYI, I did 3 years at each gravity because brewers friend suggested 5... 3 is more than 1... 5 seemed too much, especially since they were all the same.