You were right.  There are exactly four resonant frequencies per
card, and which freq vary depending on the card number.  They are in the range
of 3 to 27 megahertz, according to the book.

	There are twelve bits used to specify the facility number!  And there
are fifteen in the card number itself.  With four frequencies to choose
from, that's 7 decimal digits of precision!

	Thot you'd like to know.

sas