the date of the observation (19850104 is January, 4, 1985)
s
the ask price of the dollar in units of DM in the spot market on friday of the current week
f
the ask price of the dollar in units of DM in the 30-day forward market on friday of the current week
s30
the bid price of the dollar in units of DM in the spot market on the delivery date on a current forward contract
Source
Bekaert, G. and R. Hodrick (1993) “On biases in the measurement of foreign exchange risk premiums”, Journal of International Money and Finance, 12, 115-138.