On Linux I use gfblip.appspot.com, a.k.a. Blip by apenwarr. It graphs the current latency (Round-Trip Time) to my ISP router[*], and a nearby internet server, so I can compare the two.
Blip is amazingly useful. Mainly because it can immediately distinguish issues with local wireless, from issues with the ISP connection. This is an important first question when diagnosing network issues. And it's a web app, I don't even have to install it! On my laptop, Blip can load from my browser's cache even if the internet is totally unreachable.
(One example: when the issue is one long download stream v.s. massive bufferbloat in the ISP router, I see the latency sawtooth on the internet part only).
So I find this feature of blip very useful. Unfortunately it is not available everywhere I try to run it. Running Blip on another computer which has Windows instead of Linux... IIRC Blip doesn't work properly in Microsoft Edge. Google Chrome was available on the Windows computer, but Blip is not able to ping the local router - it instead graphs the latency to gstatic.com.
Each time on that computer, I reach for my beloved Blip. Then I spend far too long confusing myself. Blip isn't doing what I'm used to, so I mis-diagnose and chase after a red herring.
[*] Yes really, the web app pings your router. For an outline of how this can possibly work, see the README. Admittedly this assumes your router uses one of the most common private IPv4 addresses (due to NAT).
How can I fix my habitual procedure, to reliably cover Windows PCs?
This doesn't need to work around locked-down corporate machines. It may involve multiple different options, though I might still want to compare between machines of different types.
Presumably this procedure will involve one or more pieces of software :). I'm asking here instead of superuser.com, as the choice of which software seems too subjective.
The solution may involve me doing a bit of rote memorization, and that's fine. I'm not a frequent Windows user right now, but I'm very interested in this area.