  We developed a compact and easy-to-use phase meter based on a zero-crossing
counting algorithm for digitized signals. Owing to the algorithm, the phase
meter has low-noise and wide dynamic range. Low-noise differential phase
measurements can be done for square waves (-204 $\mathrm{dBrad^{2}/Hz}$ for a
1-kHz, 1-$\mathrm{V_{p-p}}$ signal, 10 Hz-1 kHz offset, with cross-correlation)
as well as sinusoidal waves, with a measurement error of $<1 \times 10^{-4}$
rad. We also demonstrated a direct phase measurement of an optical-beat note
from a free-running laser over 10 decades (0.25 mHz-10 MHz) with a wide dynamic
range of ~280 dB at 0.25 mHz. The phase meter can be an alternative for
conventional phase meters and frequency counters in wide range of experiments.
