The chart shows the number of stars for some faintest star over the entire sky. Stars up to 4.5 mag are visible to the naked eye in the city. In the country up to 6 mag (corresponds to approx. 5000 stars for northern + southern sky). An opera glass allows observations up to 8 mag. With the binoculars stars up to 10 mag can be observed (depending on the lens aperture). A telescope with an objective diameter of 200mm (8 inches) and 29x magnification reaches the limit size of 14 mag. Depending on the observation location (light pollution), phase of the moon, experience and age of the observer, the faintest star can differ from the actually observable sky by 1-3 mag.
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The difference of brigthness between two faintest stars (e.g. 5 and 6 mag) is 2.512x.
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Planetensuche contains all stars up to 6 mag. After that only partially, because of this the number of stars no longer increases exponentially towards the end.