Common Power Amp Resistance Watt Formulas

P is Power, also known as Volts, also known as Electromotive Force (EMF).
I is Resistance, measured in Ohms
E is Amps, also known as Current
W is Watts, the multiplication of Power and Amperes.
kW is kilo-Watts, also known as 1000 Watts
kWh is kilo-Watt Hours, which is how many Watts are used in 60 minutes.

P = W / E
I = P / E
E = W / P
W = P * E

Alternatively:

Volts = Watts / Amps
Ohms = Power / Amps
Amps = Watts / Volts
Watts = Power * Amps

Use mogrify to rotate and scale your images on the Linux command line

First, make sure you have ImageMagick installed:

#Ubuntu/Debian
sudo apt-get install imagemagick

#RedHat, Fedora, CentOS
sudo yum install imagemagick

After that, it's super easy.

mogrify -resize 800 -rotate 90 image.jpg

The above command would resize image.jpg to 800 pixels wide maintaining aspect ratio and rotate the image 90 degrees clockwise.

To define your own dimensions (discarding aspect ratio) use the following: