The article questions the translation of a particular legal statement, a rule of calculation of personal rights, into a computer program, able to activate the rights of the concerned citizens. It does not adopt a theoretical perspective on the logic of law and computing, but focuses on contemporary welfare states, by studying the case of the calculation of housing benefit in France. Lacking access to Cristal, the source code of the calculation, we replicated the code base and met with the writers of the housing law in the ministries to conduct a critical investigation of the source code. Through these interdisciplinary methods, we identified three types of unnoticed micro-choices made by developers when translating the law: imprecision, simplification and invisibilization. Theses methods also uncover significant social understanding of the ordinary writing of law and code in the administration: the absence of a synoptic point of view on a particular domain of the law, the non-pathological character of errors in published texts, and the prevalence of a frontier of automation in the division of bureaucratic work. These results from the explicitation of programming choices, lead us to plead for a re-specification in the field of law and informatics and a reorientation of the investigations in the field of sociology of law.