Can anyone suggest a way to measure time and tempo more accurately and consistently than the timer and realtime objects? My sense is that it needs to be done in the audio realm but I haven't been able to suss out the method. I'm writing for libpd, so it needs to be compatible with Vanilla. Thanks!

Hello Gary,
You are right about the audio realm, especially as so many users of pd are processing audio.
If you have dsp on, then pd uses the sample rate to fix its timers, so [metro 1] will send a bang every millisecond based on exactly 44.1 samples if your soundcard is set to 44100Hz.........etc.
So with dsp on everything is already synced to audio, unless you stress your system to the point where it is dropping samples.
If dsp is off then [metro] will use the cpu clock.