BIO, a tiny biorhythm calculator, by Joe Horn.

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³ Mini-instructions: Your birthdate, BIO; ³
³ then NXT, NXT, NXT...                   ³
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Here's a tiny, bare-bones biorhythm generator designed to impress the
gullible natives.  And it's the only one I've seen that does not
change (nor depend upon) the DEG/RAD/GRAD mode.

The BIO directory contains three programs:

'BIO' (calculates today's biorhythms)
INPUT: Your birthdate in HP 48 date format (e.g. use 8.191992 for
       August 19, 1992; Europeans use 19.081992).
OUTPUT:
  4: BD: your birthdate
  3: Physical: -100 to 100
  2: Emotional: -100 to 100
  1: Intellectual: -100 to 100

'NXT' (to see the NeXT day's biorhythms)
INPUT: The output from 'BIO'.
OUTPUT: Same as 'BIO' except the birthdate will be one day earlier,
  making you one day "older", thus effectively calculating tomorrow's
  biorhythms for you.
This is mostly useful to see if each cycle is rising or falling.

'BRY' (biorhythm subroutine)
Used by 'BIO'; not intended for use from keyboard.
INPUT: number of days since birth, and length of biorhythm cycle.
OUTPUT: biorhythm value (-100 min to +100 max; 0 = "critical" day).