The present invention relates to an equipment, device (10; 110) and apparatus for applying electrical stimuli to a system and acquiring a system response. According to the present invention there is provided a test equipment such as a portable test device (10; 110) for testing a system, the equipment comprising: signal generation means, signal receiving means, and signal processing means, wherein, in use, the signal generation means generates a signal to be applied to a system to be tested and the signal receiving means receives a response signal of the system, and the generated and response signals undergo processing by the signal processing means so as to provide a measure of a characteristic of the system, wherein further the generated signal comprises a plurality of periodic signals each of different frequency and phase and which are applied to the system simultaneously. The equipment finds particular use in the field of dentistry, but also finds other uses, e.g. in medicine and also in corrosion detection and battery testing.