A fixed pitch, and you hum into it. Find the unison, leave it, come back. The page holds the tone and keeps the minutes, and it does not keep the accuracy, because the beating between your voice and the drone is the readout and a number would be a score.
The drone
12:00
Start the tone, then hum into it.
Live only
Nothing here is recorded. Turn the microphone on if you want a needle; the beating in your own ears does the same job and does it better.
If the reference choice looks like a question this page is taking a side on, it is not: see the limit below.
Minutes
The honest limit, stated first. Raga time theory is a north Indian codification of relatively recent vintage with pedagogical and nationalist motives behind it, not an ancient universal law, and the study usually cited for raga and mood found listeners tracking tempo, register and melodic complexity, which work in any music. The drone's real effect is unmysterious and is the reason it is here: a fixed reference makes small deviations audible, so attention has something to fail at continuously. On the frequency side the limit is sharper and it is not that people believe nonsense. The ancient solfeggio frequencies are a 1999 American paperback, the syllables they are pinned to are eleventh century relative pitch names carrying no frequency values, the unit was named in the twentieth century, and the story about a propaganda minister imposing the standard pitch traces to a named partisan publisher. A field with real modest evidence was buried under fabricated numbers, because the numbers sell better. No controlled evidence either way exists for 432, which is why both are on the menu and neither is recommended.