This R package defines an S3 class `units` that attaches measurement units (e.g., meters, seconds, kg) to numeric vectors, matrices, and data frame columns. It provides automatic unit propagation, conversion, derivation, and simplification through arithmetic operations, built on the UNIDATA udunits2 C library. The package integrates with ggplot2 for axis/scale labeling, supports conversion to/from difftime and POSIXct, and offers helpers like `set_units()`, `mixed_units()`, and `keep_units()` for preserving units across operations that would otherwise strip them. It is actively maintained, with comprehensive tests, CI workflows, reverse dependency checks, and vignettes demonstrating its use in scientific and geospatial computing. While the core unit logic is delegated to udunits2, the R implementation demonstrates clean S3 method dispatch, careful handling of unit symbols, and a reusable pattern for attribute preservation.