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Orbital Eccentricity

The orbital eccentricity of an astronomical object is a parameter that determines the amount by which its orbit around another body deviates from a perfect ... more

Sharpe ratio

In finance, the Sharpe ratio (also known as the Sharpe index, the Sharpe measure, and the reward-to-variability ratio) is a way to examine the performance ... more

Pixels Per Inch (PPI)

Pixels per inch (PPI) (or pixels per centimeter (PPCM)) is a measurement of the pixel density ... more

Standard deviation calculator

Calculates the standard deviation (SD) of a series of numbers (x).
In statistics, the standard deviation (SD) is a measure that is used to quantify ... more

Pell's equation

Pell’s equation is a Diophantine equation (a polynomial equation in two or more unknowns ).
In Cartesian coordinates, the equation has the form ... more

Richardson Number

The Richardson number (Ri) is named after Lewis Fry Richardson (1881 – 1953). It is the dimensionless number that expresses the ratio of potential to ... more

Euler line (distance between the centroid and the circumcenter of a triangle)

In geometry, the Euler line is a line determined from any triangle that is not equilateral. It passes through several important points determined from the ... more

Gain of pyramidal horn antenna

A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct radio waves in a beam. Horns are ... more

Worksheet 980

PPI can be calculated from knowing the diagonal size of the screen in inches and the resolution in pixels (width and height). This can be done in two steps

Using the Pythagorean theorem, for 3 different screen resolutions:

Diagonal Resolution - Pixels

Using the Diagonal Resolution from the previous formula we calculate the PPI for 3 corresponding screen sizes :

Pixels Per Inch (PPI)


10.1 inch tablet screen of resolution 1024×600 : 117.5PPI
21.5 inch PC monitor of 1080p resolution : 102.46PPI
27 inch PC monitor of 1440p resolution : 108.78PPI

Rydberg formula - For hydrogen

The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. It was formulated by the Swedish ... more

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