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**((n-69)/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