OPUCEM: A library with error checking mechanism for computing oblique parameters OPUCEM (pronounced ö-peu-gem, with o-umlaut as in French deux) is a C library which combines formulas from a multitude of references for calculating Peskin-Takeuchi parameters S-T-U. The aim is to provide a minimum-dependence code to facilitate the sharing of formulas, such that: Article authors can provide typo-free versions of their formulas that match their published numerical results. Cross-checks are done to compare formulas in different papers directly. Reviews by any interested party is possible. Further studies can refer to a certain version of the code and future errata can easily be done