Why do the lights on the Pulse flash a few times before going solid?

The Pulse measurements can be affected by temperature change. When a measurement is taken, the Pulse will wait for the temperature to stabilise before taking the final measurement. While this is happening, the lights will flash. Once it is stable, the lights will stay solidly lit. This is also visible in the Pulse app, where you will see a measurement come in with “Stabilising” flashing in the lower right corner. This will go away once the temperature is stable and the reading will update to the stabilised version.