A femtometer (fm), also known as a fermi, is an extremely tiny unit of measurement used to express even smaller distances than a picometer. It is equal to one quadrillionth of a meter, which is 0.000000000000001 meters or 1 × 10^-15 meters. The prefix "femto" denotes a factor of 10^-15 in the International System of Units (SI).
Femtometers are typically used in the field of nuclear physics and particle physics to describe the sizes and distances involved in atomic nuclei and subatomic particles. The nucleus of an atom, for example, is on the order of a few femtometers in diameter. In high-energy physics experiments and discussions about fundamental particles like protons, neutrons, and quarks, femtometers are a relevant unit of measurement due to the incredibly small scales involved.
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.