what is "Part_FSC" in frealign v8.11?

Part_FSC refers to an estimated FSC that would be obtained if the reconstruction was masked with a tight mask that follows the shape of the particle (i.e. all the background noise is excluded). Frealign does not actually use such a mask since this would leaf to the usual masking problems, such as cut-off density and sharp edges. Instead, it uses the estimation procedure described by Sindelar & Grigorieff (2012) 3145. The estimation relies on the correct estimation of the volume occupied by the particle. Frealign estimates this volume as part of the above mentioned procedure. However, users are encouraged to check that this estimate is approximately correct. If it is not, the Part_FSC table will also not be correct. Provided the volume estimate is correct, the Part_FSC curve should be the correct resolution indicator for features within the particle envelope. Please see the above reference for more details.