This paper is an inquiry into the practice of what we term ’standard physics laboratory work’ in upper secondary school. We apply the concept of ‘didactical contract’ and ‘custom’ in analyzing the practice of three different Danish secondary education physics classes. The purpose is to characterise the set of ‘common rules’ that students necessarily infer from this practice and come to rely on in subsequent physics education laboratory settings that resemble those they have previously encountered – for instance when they start studying physics at university level and find the physics laboratory course-work resembling that of their upper secondary education. We argue that these common rules, i.e. the students’ prior experience ex- and implicitly relevant to the activity, will have to be explicitly addressed if alternatives to the traditional type of physics laboratory activities are to be smoothly implemented.