At the national level, laws and agreements were important instruments. Work environment design was treated in detail in the rules and regulations produced by the Swedish National Board of Occupational Safety and Health in collaboration with trade unions and employers' organizations, among others. Legislation was one way at the national level of improving the work environment. Working conditions must be adapted to human physical and mental aptitudes. The aim must be for work to be arranged in such a way that the employee himself can influence his work situation. The trade unions - at both local and national levels - initiated research and investigations in the area of work environment and computers. Guidelines for local union work were set out in national agreements. The National Board of Occupational Safety and Health formulated directives, codes of practice and regulations on aspects of particular importance to people's psychological situation.