Jim is partially correct. The EQ or equalization is set for 70 for chrome and metal tapes, and 120 for conventional tape, as I recall. The bias is some Nak proprietary coding, but is probably EX for conventional, SX for chrome and ZX for metal. I'm surprised that your blank tapes don't say something like high or low bias, and give the recommended EQ.
Question about cassette player settings
Bought a used Nakamichi cassette player (LX-5) with no manual. The player offers 3 Tape Selections - EX, SX, and ZX. I'm familiar with Type I, II and IV tapes, but not with the Nakamichi settings. What do I use? Also, the player offers 2 EQ settings - 70 and 120. Again I'm at a loss about which to use since neither my pre-recorded nor blank tapes indicate an EQ setting. Can anyone give me some guidance? Thanks and have a Merry Christmas.