I hooked up two analog signal generators to the XY inputs of the HP 1338A Tri-Color XY display to display a Lissajou curve as a test of the inputs, and posted a video.
The analog signal generators don’t have very stable frequency, so I can’t demonstrate Lissajou curves (also known as Bowditch curves) as well as I’d like, but it does show that the XY inputs work.
The signal generators are set for approximately 500 Hz and 1500 Hz sine waves with 1V P-P output (verified on oscilloscope). 1V P-P should produce full-scale deflection on the 1338A, but it is not, so possibly the input gain controls need adjustment. On the other hand, I didn’t use 50 ohm termination with the oscilloscope, and the 1338A is probably set for 50 ohm input impedance, so that may explain it.