This work presents a usability evaluation performed during the field-test of a speech based data-entry system. The application domain is the data-entry of personnel absence records from a huge historical paper archive. The system was tested by 12 employees of the personnel office of a public administration. The evaluation, based on the well known usability engineering paradigm, analyzed five human factors of the user interface: i.e. learnability, memorability, errors, efficiency and satisfaction. Evaluation measures were taken through a questionnaire and by logging usage of the system during a period of five months.