So the logging interval is set by sending a number of seconds to the meter, so the firmware can handle it. The limitations are in the app. I chose 0, 1 second, 10 seconds, 1 minute and 10 minutes because they sounded sensible, but behind the scenes the app is just saying “set logging interval to X milliseconds”. If you’re interested in adding another button that would pop up a little window where you can put in a custom number of milliseconds it should be pretty easy, the file is LoggingPreferencesActivity.java.
Also, if you’re concerned about battery life, you won’t get much better performance moving from 1 second interval to 2 or 3 seconds. The reason is that the meter has an internal reference that takes about 2 seconds to settle, so if the interval is shorter than the settling time of the reference the meter basically never turns off.
Hope this is useful, best