Error codes were displayed on a two-digit seven-segment display (one of the first seen, and built with lamps rather than LEDs). The range of error codes included not only decimal and hexadecimal digits (as seven-segment displays are commonly used) but also a limited set of other letters; for example, "P3" was one of several printer error codes. A thick manual that came with the System/3 aided the operator in interpreting the error codes and suggested recovery procedures. The System/3 had no audible warning device, so a program that was not printing, reading cards, or causing other obvious activity could halt and the operator would not know it unless he or she happened to look at the status display. Models with the Dual Program Feature had two separate status displays.