What is the bonus scale?

The combo bonus scale at the top of the screen shows you the multiplier level you have for the points you will earn from finding objects. You will increase the bonus level every time you find an object. But it will then decrease over time. Finding objects before the time runs out on the bonus scale will help increase it. The faster you find the objects the more the bonus level will increase and the more points you get.

There is also a Max combo booster that you can earn or buy that will let you start a scene with the combo scale at maximum.