# 4Pi

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> Source: https://en.wikipedia.org/wiki/4Pi
> Source revision: 1275166392
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**4Pi** may refer to:

- [IBM System/4 Pi](/source/IBM_System/4_Pi), a family of avionics computers
- [4Pi microscope](/source/4Pi_microscope), a microscope that uses interference and fluorescence computers
- 4×π = 12.56637..., the [solid angle](/source/Solid_angle) of a complete sphere measured in [steradians](/source/Steradian)
- [Hermetic detector](/source/Hermetic_detector) (also called a 4π detector)

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Adapted from the Wikipedia article [4Pi](https://en.wikipedia.org/wiki/4Pi) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/4Pi?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.