Formal specifications in \textsf{Alloy} are organized around user-defined data domains, associated with \emph{signatures}, with almost no support for built-in datatypes. This minimality in the built-in datatypes provided by the language is one of its main features, as it contributes to the automated analyzability of models. One of the few built-in datatypes available in Alloy specifications are integers, whose SAT-based treatment allows only for small bit-widths. In many contexts, where relational datatypes dominate, the use of integers may be auxiliary, e.g., in the use of cardinality constraints and other features. However, as the applications of \textsf{Alloy} are increased, e.g., with the use of the language and its tool support as backend engine for different analysis tasks, the provision of efficient support for numerical datatypes becomes a need. In this work, we present our current preliminary approach to providing an efficient, scalable and user-friendly extension to \textsf{Alloy}, with arithmetic support for numerical datatypes. Our implementation allows for arithmetic with varying precisions, and is implemented via standard \textsf{Alloy} constructions, thus resorting to SAT solving for resolving arithmetic constraints in models.