Well, I find it extremely useful.

This is my new go-to item when someone asks me, "What would you bring with you if you could go back in time to the year 1600?"

I thought I was the only one who pondered that! I think we'd have even more fun times in 1st century CE Alexandria.

They'd burn you at the stake.

This comment got me thinking: if that were to happen unexpectedly, how would you

1) determine when and where you were, and

2) convince the locals who probably don't speak your language or look like you not to kill or imprison you?

3) Live for more than a few days, with bacterial fauna of that time being so different, your immune system, completely unpolished for those type of bugs, would probably hold out for only a very short time.

Your immune system carries memories of those days.

With antibiotics prevalent that memory may be fuzzy

Wouldn't a book on microbiology be much more useful to humanity?

I have a copy of The Handbook of Mathematics, which is kind of a similar idea done commercially. It's genuinely useful, but the thing is that it's HUGE, well over 1000 pages. The main reason for this is that it is organized and fairly comprehensive, it's more of a reference than a cheat sheet. It has enough detail and depth that you can actually count on it to remind you of a subject you haven't had to use in a while.

The post here is really more like a true cheat sheet. Random topics and formulas thrown together without much organization or depth. You need to remember quite a lot already to be able to actually make use of any of this information, which to me kinda defeats the purpose. Another big problem is consistent and well-defined notation. This looks like it's copied and pasted from a lot of different sources, so you are going to have a bunch of different notational conventions that you will need to be conscious of.

I'm hoping that this work might give me some valuable info on how to get started on various Project Euler[0] problems that I might otherwise have no idea how to approach, or that I wouldn't know what area of math to do research for.

[0]https://projecteuler.net/

This is exactly what I thought. In fact, when I got to the section that listed the right-truncatable primes, I immediately searched Euler because I knew there was a problem about them -- turns out I had already solved it though lol.

My advisor had material of this sort (eg lots of Runge Kutta schemes and theorems about RK conditions; also books of ODE/PDE solutions. It came useful when we were working intensively toward the end of my thesis.

This comment reminds me of the archetypal high-school student who asks "when are we ever going to use this stuff?"

If you have to ask...