1 Jan 1966 to 31 Dec 1966
US foreign surface letter rate 11 c
Swedish foreign surface letter rate 60 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 60 and rounded up to nearest 5 öre was normally paid by affixing stamps on the item.
Air mail letter with 10 cent. Correct rate 15 cent. Shortpaid 5 cent. US due handstamp indicates double deficiency 2x5=10 cent and foreign letter rate 11 cent. In Sweden 10/11 of foreign letter rate 60 öre = 54.55 öre rounded up to 55 öre has been charged. Normally the amount was paid by affixing stamps on the item but here the due amount probably has been paid in some other way.