3S5
The Tektronix Type 3S5 is a sampling time base plug-in introduced in 1968 for 560-series scopes. It takes two S-series sampling heads such as the S1, S2, S3. S4, S5, or S6. It is particularly designed to be used in 567 and 568 scopes, where it is programmable and provides signals that inform the digital unit of the scale factor and units, depending on what sampling head is inserted.