I think you're confused

Cust: I want a black bikini in a 28JJ
EM: sure (writes down 28JJ on a notepad in front of cust) is it just the bikini you want in the double J?
Cust: yes
EM: I'll have a look for you

(Goes into stockroom, there is only a K or a HH)

EM: the closest I've got is a K
Cust: thats going to be far too big
EM: it's one cup size bigger than this (holds up paper so cust can see) or its a HH which is going to be two cup sizes smaller
Cust: have you got an F?
EM: an F? Thats seven cup sizes smaller than the double J you wanted...
Cust: I'll try it

(EM goes into the stockroom, theres a double F)

EM: try this one...

(Later)

EM: how did you get on?
Cust: it's a bit small but I'll take it
EM: ok...