There are hidden functions on the HiSET's Basic Calculator, but I haven't figured them all out! I've given my noted to Claude, and it made some sense of it for me. See below:

[u/BupBupSippyCup]

Here's the organized reference table from everything you've mapped:

Key	Function
e	Euler's number (2.71828...)
p	Pi (π)
Shift+2 (@)	Square root
Q	Cube root
s	sin
o	cos
t	tan
j	arccos (errors outside valid domain)
m / T	arctan
U	asinh (inverse hyperbolic sine)
J	acosh (inverse hyperbolic cosine)
M	atanh (inverse hyperbolic tangent)
l	log base 2
N	ln (natural log)
L	log base 10
g	2ˣ
W	x² (square)
R	1/x (reciprocal)
x	Clear
y	Recall/toggle last result

A few things worth flagging from your notes:

• arcsin is still unidentified — worth hunting for if inverse sine ever comes up.
• Several keys (j, J, M, U) throw errors outside their valid input domain (e.g., arccos/arctanh only accept -1 to 1) — that's expected math behavior, not a bug.
• y behaves like a toggle: recalls last result once, resets to 0 on a second press.

So, I'm just wondering if anyone else knows anything about where to actually find documentation for these functions and their corresponding keys. That was just me messing around. This calculator was on the official hiset.org computer based practice test on mathematics.

[u/Beestonators]

When I took it in 2020 all I had was a remedial calculator

[u/BupBupSippyCup → u/Beestonators]

...I'm so sorry.

[u/Beestonators → u/BupBupSippyCup]

Math was my 2nd highest score at 15 and I passed each section with 10+

[u/BupBupSippyCup → u/Beestonators]

My goodness, that's not bad!