The Type W Plug-In Unit is a high-gain calibrated differential comparator designed for use in all Tektronix Type 530-, 540-, 550-, and 580-Series Oscilloscopes and their rackmount equivalents. The W Unit can also be used in conjunction with other oscilloscopes and devices through use of the Tektronix Types 127, 132, or 133 plug-in power supplies. The primary operating modes for the unit are: (1) conventional plug-in preamplifier, (2) differential input preamplifier, or (3) differential comparator. Passband of the W Unit depends upon the oscilloscope used with the unit (see Table 1-1). When the unit is used with a Type 540-Series Oscilloscope at a sensitivity of 1 mv/ cm, the maximum passband capability is dc to 8 me, increasing to dc to 23 me at 50 mv/cm. As a differential input preamplifier, the dynamic range of the W Unit permits common-mode signals up to ±15 volts in amplitude to be applied to the amplifier without attenuation. With a rejection ratio of about 20,000 to 1 for dc or low-frequency signals, small signals of 1 mv or less on large common-mode signals can be measured. Common-mode signals which exceed the dynamic range of the W Unit can be attenuated before being applied to the amplifier by means of an input attenuator. As a differential comparator, voltage measurements using the slide-back technique can be made with this unit. The high accuracy and stability of the dc comparison voltage added differentially to the input signal makes precise voltage measurements possible. Using this mode of operation, the W Unit has an effective screen height of ±11,000 cm. This is equivalent to a ±11-volt dynamic signal range at a maximum sensitivity of 1 mv/cm. Within this range, calibrated ±dc comparison voltages can be added differentially to the input signal to permit a maximum of about 0.001 % or 100 /iv per mm to be resolved.