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2025

Introducing Absolute Quantities

An absolute quantity represents an absolute amount of a physical property — measured from a true, physically meaningful zero. Examples include mass in kilograms, temperature in Kelvin, or length in meters (as a size, not a position). Such quantities live on a ratio scale and have a well-defined origin; negative values are typically meaningless.

Absolute quantities stand in contrast to:

  • Affine points (e.g., \(20\ \mathrm{°C}\), \(100\ \mathrm{m}\ \mathrm{AMSL}\)) — values measured relative to an arbitrary or conventional origin.
  • Deltas (e.g., \(10\ \mathrm{K}\), \(–5\ \mathrm{kg}\)) — differences between two values.

Arithmetic on absolute quantities behaves like ordinary algebra: addition, subtraction, and scaling are well-defined and map naturally to physical reasoning. This article proposes making absolute quantities the default abstraction in mp-units V3, reflecting how scientists express equations in practice.

Note: Revised October 31 2025 for clarity, accuracy, and completeness.

Bringing Quantity-Safety To The Next Level

All quantities and units libraries need to be unit-safe. Most of the libraries on the market do this correctly. Some of them are also dimension-safe, which adds another level of protection for their users.

mp-units is probably the only library on the market that additionally is quantity-safe. This gives a new quality and possibilities. I've described the major idea behind it, implementation details, and benefits to the users in the series of posts about the International System of Quantities.

However, this is only the beginning. We've always planned more and worked on the extensions in our free time. In this post, I will describe:

  • What a quantity character is?
  • The importance of using proper representation types for the quantities.
  • The power of providing character-specific operations for the quantities.
  • Discuss implementation challenges and possible solutions.