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I am learning photography and looking to buy a flash. I learned the basics of the flash, and as far as I saw everywhere, the Guide Number had a feet unit with the ISO number; e.g. 160' at 100 ISO.
I came across this format and I don't know how to interpret it — it displays the feet, ISO and another distance. See for example https://www.bhphotovideo.com/c/compare/Yongnuo_YN685_vs_Yongnuo_YN-560-IV/BHitems/1247484-REG_1101196-REG
I don't understand what it means by 196.85' (60 m) ISO100 at 200 mm position or 190.29' (58 m) ISO100 at 105 mm position. Can someone please help me interpret this?