US foreign surface letter rate 18 c
Swedish foreign surface letter rate 110 öre
US handstamp shows amount to pay in US cents (normally double deficiency) and US surface letter rate.
In Sweden the indicated fraction multiplied by 110 and rounded up to nearest 5 öre was normally paid by affixing stamps on the item.
Letter with 16 cent. Correct rate 18 cent. Shortpaid 2 cent. US due handstamp indicates double deficiency 4 cent and foreign letter rate 18 cent. Swedish due 4/18 of 110 = 24.44 öre rounded up to 25 öre has been charged. The amount has probably been paid together with other fees.