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.
Single rate air mail letter with 18 cent. Correct rate 20 cent. Shortpaid 2 cent. US due handstamp indicates double deficiency 2x2=4 cent and surface letter rate 13 cent. The fraction 4/13 multiplied by Swedish foreign rate 70 öre = 21.54 öre rounded up to 25 öre has been indicated on the due label. The amount has probably been paid on another document.