Thread: a problem while picking phase arrival in PLOTPK window

Dear All:
When I try to picking phase arrival in plotpk window,
I type ohpf to create a hypo file before phase picking.
I can get correct P-phase arrival time after I typing "P" to decide the P-phase,
however, I cannot get S-phase arrival time when I type "S" to decide the S-phase,
the arrival time of S-phase reveals 0.0 both in the PPK window and in the hypo file.
how can I resolve this problem?
Thanks all for your help.