To minimize the record keeping efforts and errors, a direct interface between a measuring instrument and a microcomputer is helpful. Many instruments provide data with an analog signal; to convert an analog signal to a digital signal, an A/D converter is needed. A number of factors govern the choice of A/D converter for a particular application: the number of instruments that can be connected to the device, the number of individual states an analog signal can be discretized, and the conversion rate, which hinges, in part, on whether the data transmission is serial or parallel. An A/D converter should match most closely the voltage of an instrument; in many cases, some form of signal conditioning is necessary to achieve this. To show how traditional instruments may be converted using an A/D converter, an example is given of connecting a conductivity meter to a portable microcomputer. A program that acquires data once per minute and prints the results on the microcomputer screen is given in its entirety for both laptop and notebook computers. A partial list of manufacturers of A/D converters, with addresses and telephone numbers, is given.