I can understand why she did not know. Weight was probably taught at primary school and referred to as grams and kilos so no need for an abbreviation and would have no knowledge of lbs.
Very few people buy loose items by weight and certainly not a 20year old.
I dare say that a 20-year-old knows a lot more about tech and things relevant to the younger people's world today than I do so I would not be critical going down the young people today route.
Cookery books and other books - are you keeping them ?
How many pair of twins have you met?
Mistreated by the NHS and don't Know Why - Very Upsetting!
Daughter not allowed to know new baby’s name until she visits him
I’ve never found it a problem though, apart from having to google what’s normal when I’ve checked a DGS’s temperature. 98.6 is still my go-to (wasn’t there a song about it?).