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.
In the field of atomic and molecular physics, an "atomic unit of length" is a unit of measurement that is used to express distances at the atomic and molecular scale in a dimensionless way. It is part of a system of atomic units (a.u.) that simplifies calculations involving fundamental physical constants and properties of atoms and molecules.
The atomic unit of length (a.u. of length) is defined in terms of the Bohr radius (a₀), which is a fundamental constant in atomic physics. The Bohr radius is approximately 0.52917721067 angstroms (Å) or 5.2917721067 x 10^-11 meters (m).
In atomic units, the Bohr radius is set to exactly 1 a.u. of length. Therefore, when using atomic units, distances are expressed relative to the Bohr radius, and the value of 1 a.u. of length corresponds to the typical size scale of atomic and molecular structures.
The use of atomic units simplifies many quantum mechanical calculations and allows physicists and chemists to work with dimensionless quantities, making it easier to compare and analyze atomic and molecular properties.