I should point out that the N64 version of 240p Test Suite was the basis for redesigning all the other 240p Monoscopes.
Once I understood how close to 100% NTSC video the N64 could produce. I knew it was going to cause issues with setting the correct amount of overscan.
The vast majority of CRTs have overscan between 7%~10% of the full NTSC video area. Or 90%~93% viewable area as I prefer to think about it.
The neat thing about most videogame systems is the image they produce falls within the 90%~92% range already, so for the most part you should already see almost everything from most systems.
N64 is weird because it produces way more for seemingly no reason. So I decided the pattern needed to cater to the needs of the TVs themselves and communicate that clearly.
After a lot math and proportions and checking and testing, I was able to produce an image on screen that matched up exactly with 90% reference NTSC, then it was just a matter of tweaking to add the 91% line in green, then the 95% line in magenta, then the cyan line is the maximum output of the N64... something you should never ever see.
The 95% magenta line is only there for certain calibration steps for PVMs and even those get zoomed in to 93% afterwards. Which is nominally the black space between the green line and the magenta line.
Most people don't like using 93%, as it produces pillarbars on most other game systems. It's perfectly safe to zoom to 90% for CRTs and it cuts off the least amount of each game system while also eliminating any black bars.
Once I got this working, it didn't take long for me to realize I might be able to do exactly the same thing for other systems and fix a lot of issues with how we drew patterns for each system.
So enjoy, and don't hesitate to ask if you need any help.