When I was a USCG Radioman we guarded 500kcs (600 meters) as a calling/answering freq to QSY off 500 with commercial oprs to copy wx, (OBS), medicals (Medico), and, heaven forbid, an SOS. The Japanese used "r" for a period and a "t" for a zero. Catch you unawares the first time you heard it; but after that it was sorta neat!
de Allan W4EAB
"It's the journey; not the destination."