# choose the observation to track here (YYYYMMDD)
scalar target = 19700101

nulldata 518 --preserve
setobs 12 1970:02

join INDPRO.txt ip_jan70 --data=INDPRO --tkey=realtime_start_date \
--tconvert=observation_date \
--filter="observation_date==target" --aggr=seq:-1

ip_jan70 = ok(ip_jan70) ? ip_jan70 : ip_jan70(-1)
gnuplot ip_jan70 --time --with-lines --output=display