Student understanding and competency in probability have been investigated from different perspectives. Competency is often measured in the form of tests. The purpose of this study was to investigate whether perceived understanding and competency can be calibrated and assessed together using Rasch measurement tools. The study comprised 44 students who enrolled in the STAT131 Understanding Uncertainty and Variation course at University of Wollongong, Australia. Their voluntary participation in the study was through the e-learning Moodle platform where tests and assessment were administered online. Data were analysed using the Rasch measurement models. The study revealed majority of the students had little understanding about conditional and independent events prior to learning them but tended to demonstrate a slightly higher competency level afterward. Based on the Rasch map, there is an indication of some increase in learning and knowledge about probability concepts at the end of the two weeks lesson.