Simon, I think there's a printing error in Sixteen: https://i.imgur.com/KTODvLF.png
Note the "1/2 fresh Monin Pure Cane Sugar Syrup". This should, of course, be "15ml" and not "1/2 french" in order to match the recipe under "Whiskey Sour (Difford's Recipe)".
Hi Chris, ah yes, that's a typo...as you say, it is 15ml sugar syrup. Many thanks for making us aware, Simon has made a note to correct it for the next edition. So many words to proof!
https://i.imgur.com/KTODvLF.png
Note the "1/2 fresh Monin Pure Cane Sugar Syrup". This should, of course, be "15ml" and not "1/2 french" in order to match the recipe under "Whiskey Sour (Difford's Recipe)".