Clock - Broken Tenths

[Freddy]

Friday night: AD informs us of a quirk in the system. The tenths function on the scoreboard ceased to work. Tricky part was, when the clock showed 00:00, the horn would not blow until the tenths were finished, then it would go off. We asked to have it demonstrated just before the game, which helped because twice that game the whistle killed the clock, which showed 00:00, but the next play was required before the horn ended the first quarter and then the game. He said that if we needed to, we could go to the LED readout at the table and check to see if .3 or less was remaining in order to benefit from that information. Book says, "This rule does not apply if the clock does not display tenths of a second." Were we correct to avail ourselves of the LED readout of the "clock" in lieu of the scoreboard which lacked that information?