The easiest way is to install a water level app. On the iPhone, the spirit level can be used in the “tape measure” app. This app is installed on the iPhone by default. If the app shows the slope in degrees, it must be converted into a percentage. There are various free online calculators for this purpose. Without a spirit level, the slope can be calculated as a percentage by dividing the difference in height by the horizontal distance and multiplying the result by 100.
