The Note Display (from Hz) block shows which note a frequency is. It has one control input that carries a frequency in Hz and no outputs; the node shows the nearest note name, how many cents it is off and the frequency, with the same meter as the Note Display. Wire a peak detector's frequency output into it to turn the classic tuner boards into note tuners. A frequency of zero or below means no note. There are no parameters.
It does no detection of its own: each tick it passes the control value through, and the display names it as the nearest equal-tempered note with A4 = 440 Hz (anything outside the MIDI range, about 8 Hz to 12.5 kHz, shows as no note).