In all, more than 600 of the 1,688 U.S. TV stations now offer digital signals. Exactly how many depends on whose numbers you use.
Private research company Decisionmark Corp. said 670, the Federal Communications Commission said 643 and the National Association of Broadcasters said 621.
Why the discrepancy? Decisionmark searches out the latest stations; the NAB generally waits until stations or viewers notify it; and the FCC takes a similarly passive approach, but includes stations granted temporary operating permits but not necessarily on the air.
Of the 600-plus operating digital-TV stations, roughly 450 are commercial, representing just under 40 percent of the stations required to be digital now. The rest are public outlets, which aren't required to go digital until May 1.