Comparability of clinical and research data sets may be undermined if the instruments used to acquire them vary. Even when standard 12-lead electrocardiographic formats are used for monitoring, proprietary signal processing techniques and sampling intervals may differ among devices. In order to directly compare the two commercially available standard 12-lead devices with monitoring capabilities, bifurcated wires from a single standard lead set were attached to each device in elective angioplasty patients. Neither device was used as a standard; rather, a method was designed to analyze the output from each device independently, and then, if results differed, data from both monitors were reviewed by consensus to determine the source of the differences. Analysis endpoints for each study included study quality, baseline ST-segment levels, the presence of ischemia, number of ischemic episodes, peak lead location, and peak lead amplitude. Sources of differences in these endpoints visible to consensus review included variations between devices in baseline stability, noise/artifact levels, stability of the QRS complex onset, and temporal sampling intervals.