What is a Dimensionless Constant?

# What is a Dimensionless Constant?

An example of a constant is **C**, the speed of
light, in Einstein's famous

E = M C ²

**C** is a speed, so it has *dimensions* of distance per
time. For example, it has a value of about 186,000 miles per second,
or 300,000,000 meters per second.
A dimensionless constant like **Pi** is different. Pi is
3.14159... regardless of whether you are measuring in miles, or
in meters, or in carob seeds.

Last modified: 5 July 1997
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