I ran across this on another forum. We know about various ways and tools to help synch the carbs. The other forum poster likes to use the shorting method to synch the carbs. This requires looking at the RPM of the running cylinder and comparing that to the RPM when the opposite cylinder is shorted. You make adjustments to get the RPMs the same when one cylinder is shorted.
He said that he uses an app on his phone that gives BPM or beats per minute. Something he uses for his music. BPM can essentially RPM and might be another way of comparing the performance of each cylinder during this synching process. This might be especially useful for older bikes with no tachometer.
The Android app is called "BPM Tap". I haven't tried it myself, but have downloaded the app. I'll be interested to "calibrate" it with my /7 and see what it tells me about RPM on my R69S.