New constants can be introduced with the let keyword:

let pipe_radius = 1 cm
let pipe_length = 10 m
let Δp = 0.1 bar

Definitions may contain a type annotation after the identifier (let Δp: Pressure = 0.1 bar). This annotation will be verified by the type checker. For more complex definitions it can be desirable to add type annotations, as it often improves readability and allows you to catch potential errors early:

let μ_water: DynamicViscosity = 1 mPa·s
let Q: FlowRate = π × pipe_radius^4 × Δp / (8 μ_water × pipe_length)