Deflection blanking

Oscilloscopes have two main ways to avoid drawing on the screen between traces.

One is to turn off the CRT beam by making the CRT grid negative (e.g., −150 V) relative to the CRT cathode.

Another way is to leave the CRT beam on, but to deflect it away from the CRT phosphor. The latter approach is called deflection blanking. Deflection blanking is used in several Tektronix instruments, including the 321, 422, 503, 504, 561, 564, 565, 567, and 661.