Here is a sample setup of the VMA Video Pattern Generator:
I am using a USB to HDMI adapter that goes to an external LCD monitor (Feelworld). It has an HDMI output port, which goes into a Blackmagic HDMI to SDI converter. From here it goes to the Harris Videotek CM91 and from there to the Hamlet Monitor Scope 9000.
I used this kind of setup to verify the generated test pattern. I found out that the USB HDMI converter outputs a higher brightness than the originally generated images, hence it is necessary to adjust the brightness slider from 127 to 45. Also, the signal has not the correct purity, which is visible in the vectorscope images, where the curves should be straight lines. This is not a fault of my software! It rather shows the (low) quality of the USB to HDMI converter.
With the HDMI output of my GeForce RTX4070 TI, the image is not perfect, either. That is because you can configure the graphics card output and the standard configuration (brightness, saturation, "game mode", HDR, etc.) all change the actual image output.
This is to say that handling a perfect image is not straight forward and this is the reason software like mine (VMA Video Analyser and VMA Pattern Generator) exist, along side with Waveform Monitors and Vectorscopes.