The paper describes the development of the computer literacy scale (CLS), an objective knowledgetest estimating the ability to understand ICT related symbols, functional elements and interactionpatterns as an essential aspect of computer literacy that reliably predicts successful ICT interaction.The original version (CLS-ST) was developed as a paper & pencil questionnaire and has been used ina variety of studies including older participants. The second version (CLA-IA) allows for theassessment of procedural knowledge in online work samples. The third version (CLS+) adds moredifficult items to extend the measurement range to more proficient users. For the fourth version (CLSadaptive), still more items were added and those items that fit the Rasch model were selected for theitem bank used in the adaptive version of the CLS, which reduces testing time to under five minuteswhile maintaining high reliability.