The sana critica system is midway between the first two in that the law does not specify the effect that should be assigned to a given piece of evidence, but nor is it left entirely to the free assessment of the EDRB. Instead, the EDRB must state the reasons or justify why it attributes probative value to each of the elements in the record. 511. Very few electoral codes and laws define the systems for weighing evidence that should be observed by the respective EDRBs in the cases that come before them. Some countries have adopted the free evidence system, several have established sana critica rules and a few more have a mixed system. 512. Among the greatest impacts of the introduction of electronic voting systems is their impact on the different EDRMs. The challenges that arise in this context relate to ascertaining and weighing the evidence, and to the mechanisms by which challenges will be resolved. In countries where the challenges are resolved by regular courts which are part of the judicial branch, these issues may need to be regulated by special provisions that require reform to the law. Investigating and assessing these aspects effectively may require special training for the staff of the EDRB. The rules for weighing electronic or digital evidence should be reviewed and, similarly, require the adoption of special measures or reforms. Box 7.8. Electronic voting and electoral dispute resolution: California Avery Davis-Roberts Electronic voting in California is not subject to special mechanisms for the resolution of disputes that might arise from its implementation. Instead, e-voting disputes are resolved through existing channels. The use of electronic voting and the resolution of disputes regarding the technology are widely reported in the press and through civil society organizations in California and in the United States more broadly. Despite recent controversies regarding voting technologies and widespread concern about their use, there remains a high degree 167 7. Basic elements of EDR systems b. free evidence systems, in which the EDRB can weigh the evidence offered, admitted and produced without any legal obstacle, so that the judge’s opinion is formed freely without impediment of any kind, particularly legal impediment; c. systems of logical and reasonable rules of evaluation and procedure for arriving at opinions or judgements (in Spanish, ‘sana critica’), in which the EDRB has the power to determine the efficacy of each of the elements in the record of the case in keeping with the rules of logic and the maxims of experience; and d. mixed systems which combine elements of these three systems.