I am kicking myself in the proverbial as I unfortunately remember my error in reading a specification review in 'Dpreview' that the camera that newbie had bought had a GN of 9.4m .... and I took m to mean metres when it was metric to difference between the 'imperial' system of working in feet and metric using metres. The results are the same which ever system you use so long as you do not mix measures LOL.
So if you convert 9.4metres to feet you end up with roughly 28 and the GN is always specified when using 100 ISO.
Up the camera's ISO to 400 and we have 56 ... which was the GN I used for most of my work, except in a DIY modification I cut out one of the two capacitors my flash had and halved the output for a GN40 and a recycling time half of normal. That was when I was shooting in competition with two or three other 'togs' as we shot people arriving at a show. After awhile one of them came over and wanted to know what 'super fast' flash I had which looked like his but shot twice as fast ... LOL
I had a switch so I could revert to full GN56 at the flick of a switch [ DPDT ] and seconds to fill up the second capacitor. Using GN56 I had to wait a wee while for it to recharge between shots but at GN40 it was topping up faster than I was shooting LOL Note I am using LOL instead of a smiley as it comes out as a square :-(