This article describes a technique for measuring the magnetic field inside a long solenoid using computer data logging. This is a new approach to a standard student practical. The design and construction of the sensors is described; they significantly reduce the cost of the apparatus. The approach of the practical is for the students to investigate how the magnetic field depends on the variables, such as current, solenoid diameter etc, rather than to confirm the equation. (Contains 1 table and 6 figures.)