This thesis was created in parts. A thesis made using this method usually consist of three parts, but for this thesis, the second and third part were combined into one larger part. The focus of the first part of the thesis was on the measurement methods of human hearing, and what technological solutions are available for people with hearing impairments. The purpose of the first part was to get familiar with not only the subject of the study, but also with the research methods used in the study. The combined second and third part of the thesis details the methods, results and conclusions of a usability study conducted on a web-based user interface of a customer information management system. The goal was to determine what usability problems exist in the current version of the target system, and to evaluate which of these problems are perceived as most critical, specifically by users working directly with customers. Nielsen’s heuristics were used to evaluate the usability of the system’s views in the selected use case. To gauge the general opinion the user base had of the systems usability, current and prospective users were asked to fill in a questionnaire with questions related to which parts of the system they already liked and where they thought improvements should be made. Finally, usability testing was conducted along with short user interviews to highlight what the actual users perceived to be the biggest challenges in the usability of the system. The questionnaires were filled in by 23 respondents. 8 users of differing experience and skill levels took part in the usability tests and the concurrent user interviews.