teaching aids A Lecture Room Digital MultimeterThis paper describes an instrument ca-] table of displaying numerical values of pH, temperature, pressure, and voltage over wide ranges. From it, even in a large lecture hall, students may take down unusually legible quantitative data from lecture experiments. The instrument has been designed to be simple and quick to operate while giving adequate response for the purpose.The heart of the equipment is a digital voltmeter giving four significant figures. To this have been added two main accessory units. One, a plug-in for the digital voltmeter which converts the parameters being measured linearly to a voltage driving the digital voltmeter, and the other, a slave display unit which duplicates the reading of the digital voltmeter on a scale large enough to be legible at distances up to 100 ft. Various probes or transducers are used in the measurement of pH, temperature, and pressure and these have been chosen to be small and easily manipulated so that they can be used in as versatile a manner as possible. The transducer for pressure measurements, however, is large enough so that variations in the level of a mercury manometer are visible to a class. Figure 1 shows the instrument demonstrating several capabilities.