A "fermi" (symbol: fm) is a unit of length used in physics to describe extremely small distances at the atomic and subatomic scale. One fermi is equal to 10^-15 meters or 0.000000000000001 meters. It is named after the Italian physicist Enrico Fermi, who made significant contributions to nuclear physics and particle physics.
The fermi is particularly useful for describing the sizes of atomic nuclei and the distances between particles within atomic nuclei. For example, the typical diameter of an atomic nucleus is on the order of a few femtometers (1 femtometer = 1 fm). It is also used in high-energy particle physics to describe the cross-sectional area of particle interactions.
In summary, the fermi is an essential unit of length for understanding the microscopic world of atoms, nuclei, and subatomic particles, where distances are incredibly small.
A "twip" is a unit of measurement used in desktop publishing and computer graphics, especially in the context of Microsoft Windows. The term "twip" is an abbreviation for "twentieth of a point," and it is used to define very small distances and sizes.
In the twip system:
1 twip is equal to 1/20th of a point. 1 point (abbreviated as "pt") is equal to approximately 20 twips.
Because a point is roughly 1/72nd of an inch, 1 twip is approximately 1/1440th of an inch (or about 1/567 millimeters).
Twips are used in various applications, including word processing, graphics design, and layout software. They are particularly valuable for precise positioning and sizing of elements on a computer screen or when preparing documents for printing. The twip system is commonly used in Microsoft Windows-based applications and the Windows Graphics Device Interface (GDI).
For example, in Microsoft Word, you can set paragraph spacing or element positioning in twips to achieve fine control over the layout of your documents.