Marking field and laboratory notebooks can be a time consuming and tedious task. This article describes a system whereby the contents of student's notebooks are assessed by testing the students on what they have included and their understanding of what has been done. It also tests the quality of the student's notes--detailed, organised notes result in higher marks than sketchy disorganised ones. The "Data Retrieval Test" is an open book test in which the notebook is taken into the exam room and questions are asked on its contents. The questions are based on what the tutor knows should have been included. A survey of third year degree students showed that this type of test is seen as a fair method of assessment. It is also popular with staff as it can reduce the marking time by up to 80%. The marks obtained by this test are in line with those obtained by more traditional methods of assessment. It can be adapted to assess students at different stages of their academic career. (Contains 3 figures.)