As I was entering Robbie's formula for converting MIDI number to
frequency into my Palm Pilot (which is where I put almost every
interesting piece of information these days  I got tired of losing
little pieces of paper!), I thought I would share this tip. There's
software called MathPad which allows you to solve just about any
formula on your Palm Pilot. You can try before you buy. See
http://www.probe.net/~rhuebner/mathpad.html.
Here's Robbie's formula, as entered into my Palm Pilot. The "n:79"
indicates that "n" is input, "f>" indicates that "f" is to be output.
MIDI note number to F
n:79
f>783.9908719635
f=440*2**((n69)/12)
Another example illustrates a very valuable feature: you can reverse
the roles of the variables without rearranging the formula. Consider
the formula for capital recovery. Given any three of the variables
i (interest), n (period in years), r (monthly payment), and p
(principal), you can calculate the fourth.
For example, how much can I borrow if I can pay $600/month for 5 years
at 7% interest? Note how this works. Since r, n, and i are input,
the principal p can be calculated without having to solve the formula
for p.
Mortgage (monthly crf)
i<0.07
n<5
r<600
x>0.01980119854035
p>30,301.196100698
x=((i/12)*(1+i/12)**(n*12))/(((1+i/12)**(n*12))1)
r=p*x
I use this tool so often that I can't live without it anymore. Anybody
interested in science or engineering should find it useful, too.
Steve McCollum
