The project From Inglis to Scots: Mapping sounds to spellings* (FITS) makes a first attempt at systematically exploiting the extensive – and often idiosyncratic – spelling variation attested in pre-modern non-standard spelling systems. The texts under scrutiny come from administrative and legal documents composed in various locations throughout Lowland Scotland between 1380 and 1500. This paper presents the methodological and technical decisions undertaken in order to construct a database of synchronic relationships between orthographic variants and underlying sounds.