Bottle-o-meter (de.mathfactory.bottleometer) on Google Play
This app uses the microphone to analyze the sound a bottle generates when blowing over the top of it and estimates its fill level. As widely known, one can generate tones by blowing over the top of any common bottle. Furthermore these tones change when the content of the bottle changes: The less content in a bottle the deeper the tone. This app records these tones and converts them to a fill level display using the so called Helmholtz Resonance Theory, which is valid for most bottles.Currently there are two possible mathematical model variants to choose from:- Theoretical model: This model is based on the shape parameters of the bottle - the inner neck diameter, the neck length and the bottle volume. These parameters must be specified prior to the measurement.- Experimental model: This model is based on the base frequency of the bottle - i.e. the frequency of the empty bottle. The base frequency can conveniently be provided to the app in hertz or through a sound sample (you'll need an empty exemplary bottle).Note that the results of this app only approximate the real fill level. Don't expect milliliter-precise results!If you encounter detection problems please review the microphone sensitivity option in the settings and/or write a problem report to bottleometer@mathfactorysoftware.com if the problem persists.