1 May 1967 - 30 June 1971
US foreign surface letter rate 13 c
Swedish foreign surface letter rate 70 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 70 and rounded up to nearest 5 öre was normally paid by affixing stamps on the item.
Double rate
air mail letter with 15 cent. Correct rate 40 cent. Shortpaid 25 cent.
US due handstamp indicates double deficiency 2x25=50 cent and surface letter
rate 13 cent. Amount due in Sweden, 50/13 multiplied by Swedish foreign
letter rate 70 öre = 269.23 rounded up to 270 öre paid by affixing
postage stamps.