Mr. E,
Thanks for your reply.
I see TWD on the instrument page of the TZTL12F (and on the data box), and on the FI-70 (where it's called "ground wind"--a new term for me).
Looking on the instrument page of the TZT9, I see only TWA and AWA, not TWD. However, TWD is available on the data box of the TZT9, which is good enough.