In SGP the size of a star image is frequently referred to as HFR (half flux radius); e.g. it is used in the HFR module or for the autofocus module. All very convenient!
I decided to see how HFR would compare to FWHM (full width half max) calculated by APP (atropixel processor software).
I made 100 exposures (10sec exposures of M44 with 7 different filters over a temperature range of 10 degrees); per exposure I noted down the HFR values of SGP and the FWHM calculated by APP.
With considerable accuracy I found that HFR is 83% of FWHM. Which is odd, since it should theoretically be only 47% (see youtube or other forums for explanation).
The only conclusion I can draw is that HFR in SGP is wrongly named that way and it should be HFD (Diameter instead of Radius -which is half of diameter-).