I see what Gorgonops is saying, but its old school, and not likely encountered in this day and age unless its a relic
personally every one I have tried it on sums the RGB values in house, course every one I have seen are missing pins 9 and 12 for the reasons given
I've never seen a mono monitor that does that, but I also don't think I've actually worked with any that had a manufacturing date later than 1990. ;^b I suppose I don't doubt that such animals exist, as they were at least making the POS-size mono monitors until, what, the early 20-aughts? (Never mind, I googled, you can still buy them new), and after the mid-90s or so you probably couldn't count on video cards recognizing the old sense line layout... but I've never seen one.
I don't think they're fixed freq, in as much as I seem to remember being able to get more than 640x480 out of them on an old PC. But I could be mixing up my terms here.
They did/do make mono VGA monitors capable of higher-than-640x480 but they were rare as hen's teeth back in the era when people actually bought mono monitors because they were cheaper than color ones. Most were plain-old VGA. (Which technically isn't quite "fixed frequency", they actually support three different frame sizes of 480, 400, and 350 lines, but they're not "multisync".) I'd be really surprised if your 9 inch sense-pin equipped monitor does better than that.
