HP 21S Stat/Math Calculator from 1989

This video is about the HP 21S, a niche statistics and maths calculator from HP's Pioneer series.
Sections of this video:
0:00 - Intro
1:22 - Physical Design
3:21 - Basic Usage
4:46 - Probability Distribution Functions
8:23 - Statistics and Welford's Method
10:27 - Built-in Library
11:30 - Summary
For those that are interested in knowing more about how to disassemble an HP 20S or HP 21S check out Logan West's video here:
- • HP 20s Calculator Scre...
For those that are interested in Welford's Method for calculating the mean and variance of normal distributions check out this link:
- jonisalonen.com/2013/deriving...
For more calculator videos check out my channel: / calculatorculture

[@MattMcIrvin]

It's remarkable that so many of even HP's entry-level calculators were keystroke-programmable. I guess that was a hallmark of theirs from the beginning.

[@CalculatorCulture]

Yes thats a good point. I guess, one advantage of the keystroke programming model it is relatively easy to use for simple use cases. If you can use the calculator you can program it.

[@idonotcomplyrevolution]

could you do a video showing off your collection of HP calculators?

[@CalculatorCulture]

Could do, maybe as a KZbin short 👍

[@LuisRodriguez-vh6fg]

Beautiful

[@40ozMonkey]

Let someone borrow my 20s in 7th grade. Never got it back😂

[@BellaRocko]

do you know how to open these up? Some of my buttons are getting soft, i.e. not clicking as loud or clear when pressed, but it still works. Just wondering if that can be fixed.

[@DerekDavis213]

They are 'ultrasonically welded'. No easy way to open them.

[@BellaRocko]

@@DerekDavis213 Thanks for the reply.

[@federicocaria7992]

Please, could you make a video of which calculator can perform hyperbolic and trigonometric functions of complex numbers?

[@CalculatorCulture]

My videos are each about a different modern or vintage calculator.

[@wernerhuysegoms9674]

I don't quite understand why the large numbers produce a Stat Math Error for SDEV. The limited precision would simply result in an erroneous value of 0?

[@CalculatorCulture]

Yeah for some data series the 21S does return an erroneous sdev of 0- for example 999,999, 1,000,000 & 1,000,001. It seems to me the internal logic to check for potential situations where Wilford method fails is not 100% accurate.

[@wernerhuysegoms9674]

@@CalculatorCulture mh my first guess is because in that case, sum(xi)^2/N is exact, while in the example in the video it is not. The 41C shows similar behaviour, OUT OF RANGE (!) for 1e5+(0,1,2) and 0. For 1e5+(-1,0,1)

[@wernerhuysegoms9674]

I was wrong. It is simply so that the SDEV calculation is carried out in extended precision (12 digits for the 41, 15 for the 42 and the other Pioneers), and when the result under the root is negative, the error is thrown. Free42 also implements the rule (amazingly) but since it doesn't use extended precision, it fails for different arguments eg. 1E17+(2,0,2)

[@CalculatorCulture]

@@wernerhuysegoms9674 thanks, that's useful to know.