Charles & Sandra Cohen
Thank you for testing ! I sing, and "DA Tuner" was already installed on my phone.
There's another app that someone else in the Club found -- Check the Google "Play Store" for apps under:
. . . Audio Frequency Counter
It may be higher accuracy.
It's also possible to use "fldigi" in "Frequency Analysis" mode. That puts a very narrow filter on the WWV carrier, and applies AFC tracking, and tells you what the center frequency of the filter is.
But I like the simplicity of a smartphone in my pocket.
. Charles / VA7CPC
PS -- thanks for all the work you do on this list!