To check your biorhythm levels(complete pseudo-science, but the graph seems interesting), on HP Prime:

Use the function app and plot 3 plots. Red(Physical): Sin((2*pi*X)/23), Blue(Emotional): ((2*pi*X)/28), and Green(Intellectual): Sin((2*pi*X)/33.

Go to Home view and use DDAYS() to work out how many days you have been alive, then go to that value on the plotted graph. That will show you your biorhythm levels for that day.

Now unless you happen to be 21,252 (the lowest common multiple of 23,28 and 33, and also the value at which the sequence of the graphs starts over again) days old, or 58 years, 2 months and a bit, then your 3 biorhythm levels will have changed from what they were the moment you were born.

Interesting idea, complete pseudo-science as I have said, but a nice way to show the use of a few functions of the calculator.

I think I first encountered bio-rhythms in the FX-501P/FX-502P Program Library (although it may also have been used in Casio's program libraries for their earlier programmables). I understand they are/were popular in Japan, as is blood type personality theory.

For reference, here is a scan by Bob Prosperi of an article in the June 1977 issue of Popular Electronics that shows six programs/games for the HP-25. The 5th one is for calculating your Biorhythm.

https://1drv.ms/b/s!AiI5Ei2M2Ja2mHMsEXfTUEZOz3Tk
(05-27-2022 07:01 PM)ijabbott Wrote: [ -> ]I think I first encountered bio-rhythms in the FX-501P/FX-502P Program Library (although it may also have been used in Casio’s program libraries for their earlier programmables). I understand they are/were popular in Japan, as is blood type personality theory.

For me, it was on the Apple ][ with a program that displayed a

GR biorhythm plot.

… funnily enough, I was thinking about biorhythm plots last week.

I had both the Casio Biolator and the Kosmos I.

Radio Shack even had one. That’s news to me.

I have a Kosmos 1 that I got from ebay many many years ago. I checked it recently and it is running just fine. The one caveat is that it only works until 1999.

About the programs from Popular Electronics, I'm impressed. I didn't think one could get a reasonable Biorhythm program using 50 steps. I will take a closer look and see if I can port it to the TI-57. It is going to be very tight.

Actually, I’ve figured out a way to extend the date range.

1901 becomes the start. For example, I was born in 1965 which is one year after a leap year, 1964. So, my birthdate becomes 1901. To expand on this, for example, 1966 becomes 1902, 1967 becomes 1903, 1968 becomes 1904, 1970 becomes 1902, 1971 becomes 1903, and so forth. I'm sure you see the pattern. Next, the year of the forecast date becomes 1902 plus your age at the forecast date. So, today, for example, as the forecast date is 1902+56 (my current age), thus, the forecast date for today is May 27, 1958.

(05-28-2022 02:48 AM)Matt Agajanian Wrote: [ -> ]Actually, I’ve figured out a way to extend the date range.

1901 becomes the start. For example, I was born in 1965 which is one year after a leap year, 1964. So, my birthdate becomes 1901. To expand on this, for example, 1966 becomes 1902, 1967 becomes 1903, 1968 becomes 1904, 1970 becomes 1902, 1971 becomes 1903, and so forth. I'm sure you see the pattern. Next, the year of the forecast date becomes 1902 plus your age at the forecast date. So, today, for example, as the forecast date is 1902+56 (my current age), thus, the forecast date for today is May 27, 1958.

Wouldn't it be simpler to subtract 40 or 60 years off the dates?

I don't have the calculator that the article refers to, but on page 46 it mentions how to use dates in a different century by using 3652500 in register 5 and using the different date format suggested. Does that not work in this century?

(05-28-2022 11:42 AM)ijabbott Wrote: [ -> ] (05-28-2022 02:48 AM)Matt Agajanian Wrote: [ -> ]Actually, I’ve figured out a way to extend the date range.

1901 becomes the start. For example, I was born in 1965 which is one year after a leap year, 1964. So, my birthdate becomes 1901. To expand on this, for example, 1966 becomes 1902, 1967 becomes 1903, 1968 becomes 1904, 1970 becomes 1902, 1971 becomes 1903, and so forth. I'm sure you see the pattern. Next, the year of the forecast date becomes 1902 plus your age at the forecast date. So, today, for example, as the forecast date is 1902+56 (my current age), thus, the forecast date for today is May 27, 1958.

Wouldn't it be simpler to subtract 40 or 60 years off the dates?

Like the old adage, someone always builds a better mousetrap.

(05-28-2022 05:45 PM)matalog Wrote: [ -> ]I don't have the calculator that the article refers to, but on page 46 it mentions how to use dates in a different century by using 3652500 in register 5 and using the different date format suggested. Does that not work in this century?

You can try

https://www.sydneysmith.com/products/hp2...index.html.

The program kind of works for this century but, even for the 1900s, it doesn't deal precisely with leap years. Instead it assumes that every February has 28.25 days. It may do additional corrections but at the end you get an approximation, actually a fractional number, for the number of days between your birth date and today. In my case it was off by 0.6 days which is not bad at all.

I was surprised they could do it within 50 steps. They can't quite but their approach seems like a good compromise.