The Tektronix Type CA is the most common plug-in for 500-series scopes. Over 50,000 were produced.
The risetime of a Type 545 oscilloscope with a Type CA plug-in is 15 nanoseconds, and the bandwidth is 24 MHz. Maximum vertical sensitivity is 50 mV/div.
Type CA is an enhancement over its predecessor, Type 53/54C, adding ADDED mode to the A, B, CHOPPED, ALT repertoire. The "A" in "CA" stands not only for the fact that it is a modified, enhanced replacement, but also because the feature added was "ADDED". It was introduced in 1959 and discontinued in 1973, making it not only the most-produced but also the longest-lived, if you include Type 53/54C.