Up to three single width modules can be plugged into the TM503A, or one single and one double width module can be accommodated. The TM500-Series of plug-ins includes oscilloscopes, function generators, scope calibration equipment, DMM's, counters and power supplies. Also choose from pulse generators, operational amplifiers, bandpass filters, and current probe amplifiers. You may be able to fit every instrument you'll need into one small mainframe.